Fix a null pointer dereference when no DNS search path is configured.
This showed up as a segfault while running the gsasl test suite.

Taken from upstream:
https://github.com/krb5/krb5/commit/cd82bf377e7fad2409c76bf8b241920692f34fda

diff --git a/src/lib/krb5/os/dnsglue.c b/src/lib/krb5/os/dnsglue.c
index e35ca9d76c..0cd213fdd7 100644
--- a/src/lib/krb5/os/dnsglue.c
+++ b/src/lib/krb5/os/dnsglue.c
@@ -91,7 +91,7 @@ static int initparse(struct krb5int_dns_state *);
 #define DECLARE_HANDLE(h) struct __res_state h
 #define INIT_HANDLE(h) (memset(&h, 0, sizeof(h)), res_ninit(&h) == 0)
 #define SEARCH(h, n, c, t, a, l) res_nsearch(&h, n, c, t, a, l)
-#define PRIMARY_DOMAIN(h) strdup(h.dnsrch[0])
+#define PRIMARY_DOMAIN(h) ((h.dnsrch[0] == NULL) ? NULL : strdup(h.dnsrch[0]))
 #if HAVE_RES_NDESTROY
 #define DESTROY_HANDLE(h) res_ndestroy(&h)
 #else
@@ -104,7 +104,8 @@ static int initparse(struct krb5int_dns_state *);
 #define DECLARE_HANDLE(h)
 #define INIT_HANDLE(h) (res_init() == 0)
 #define SEARCH(h, n, c, t, a, l) res_search(n, c, t, a, l)
-#define PRIMARY_DOMAIN(h) strdup(_res.defdname)
+#define PRIMARY_DOMAIN(h) \
+    ((_res.defdname == NULL) ? NULL : strdup(_res.defdname))
 #define DESTROY_HANDLE(h)
 
 #endif
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<tr><td><span title='2022-12-20 16:56:03 +0100'>2022-12-20</span></td><td><a href='/guix/commit/tests/guix-package.sh?id=680970490c556ae0029aa1ba2b0faba162118186'>tests: Adjust 'guix package' test to latest package search metrics.</a><span class='msg-avail'>...<span class='msg-tooltip'>With commit bbcd06e56c06376e640a7ac81a7109e7135a20f2, the command
"guix package -s '^fileutils$'" would match the 'ocaml-fileutils'
package, because its 'package-upstream-name*' is "fileutils".  Work
around it.

Reported by Vagrant Cascadian.

* tests/guix-package.sh: Change "fileutils" example to use a different
package name.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-05-23 16:24:46 +0200'>2022-05-23</span></td><td><a href='/guix/commit/tests/guix-package.sh?id=aaf547824e389b68c028c9b3fd4d15fd2991dc31'>scripts: package: Transform before creating manifest entries.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/package.scm (options-&gt;installable): Add TRANSFORM
argument, to be able to directly transform the new packages before
creating their manifest entries.
(process-actions): Remove transform-entry, and step3, transforming
directly in step2.
* tests/guix-package.sh: Add test.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Josselin Poiret</td></tr>
<tr><td><span title='2022-02-18 14:14:38 +0100'>2022-02-18</span></td><td><a href='/guix/commit/tests/guix-package.sh?id=5a57313918a5c1bd5cf8238c2dcae64a03523952'>profiles: 'profile-derivation' rejects unsupported packages.</a><span class='msg-avail'>...<span class='msg-tooltip'>Previously user-facing commands would happily start building packages
even if they do not support that system.  With this change, all the
user-facing commands reject unsupported packages without going further.

* guix/profiles.scm (profile-derivation): Add #:allow-unsupported-packages?.
Define 'check-supported-packages' and honor #:allow-unsupported-packages?.
* tests/guix-pack.sh, tests/guix-package.sh, tests/guix-shell.sh: Ensure
that unsupported packages are rejected.
* tests/guix-system.sh: Pass "--system=armhf-linux" when attempting to
build gnu/system/examples/asus-c201.tmpl.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-04-29 01:22:04 +0200'>2021-04-29</span></td><td><a href='/guix/commit/tests/guix-package.sh?id=524c9800afb433cc474132185d8e37f72004adb3'>diagnostics, ui: Adjust to 'read-error' and 'syntax-error' in Guile 3.0.6.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/diagnostics.scm (source-properties-&gt;location): Add clause for
vectors.
* guix/ui.scm (report-load-error): Tweak 'read-error' handling for 3.0.6.
* tests/guix-package.sh: Relax regexp for the "unbound variable"
diagnostic check.
* tests/guix-system.sh: Adjust "missing closing paren" check for 3.0.6.
* tests/records.scm (location-alist): New procedure.
("define-record-type* &amp; wrong field specifier")
("define-record-type* &amp; wrong field specifier, identifier")
("define-record-type* &amp; duplicate initializers"): Use it.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-03-05 12:49:27 +0100'>2021-03-05</span></td><td><a href='/guix/commit/tests/guix-package.sh?id=90ea8b16eb519a88d8f739fea5a416c0b99de19f'>profiles: 'package-&gt;manifest-entry' preserves transformations by default.</a><span class='msg-avail'>...<span class='msg-tooltip'>Previously, transformations applied from a manifest (rather than via
"guix install") would be lost.  This change fixes that and simplifies
things.

Reported by zimoun at
&lt;https://lists.gnu.org/archive/html/guix-devel/2021-02/msg00153.html&gt;.

* guix/profiles.scm (default-properties): New procedure.
(package-&gt;manifest-entry): Use it for #:properties.
* guix/scripts/pack.scm (guix-pack)[with-transformations]: Remove.
Remove caller.
* guix/scripts/package.scm (transaction-upgrade-entry): Remove calls to
'manifest-entry-with-transformations'.
* tests/guix-package.sh: Add test.
* tests/transformations.scm ("options-&gt;transformation + package-&gt;manifest-entry"):
New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-02-01 17:32:35 +0100'>2021-02-01</span></td><td><a href='/guix/commit/tests/guix-package.sh?id=9fd7b050e2198c89f0763fe79f5c541b77b8e5c9'>guix package: Add '--export-manifest'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/package.scm (export-manifest): New procedure.
(show-help, %options): Add '--export-manifest'.
(process-query): Honor it.
* guix/build/profiles.scm (build-profile): Mention it.
* tests/guix-package.sh: Test it.
* doc/guix.texi (Invoking guix package): Document it.
</span></span></td><td>Ludovic Courtès</td></tr>