Fix a regression in 2.9.12 where serializing empty HTML documents would
not add a terminating newline.

  https://gitlab.gnome.org/GNOME/libxml2/-/issues/266

Taken from upstream:

  https://gitlab.gnome.org/GNOME/libxml2/-/commit/92d9ab4c28842a09ca2b76d3ff2f933e01b6cd6f

diff --git a/HTMLtree.c b/HTMLtree.c
--- a/HTMLtree.c
+++ b/HTMLtree.c
@@ -763,11 +763,15 @@ htmlNodeDumpFormatOutput(xmlOutputBufferPtr buf, xmlDocPtr doc,
             if (((xmlDocPtr) cur)->intSubset != NULL) {
                 htmlDtdDumpOutput(buf, (xmlDocPtr) cur, NULL);
             }
-            /* Always validate cur->parent when descending. */
-            if ((cur->parent == parent) && (cur->children != NULL)) {
-                parent = cur;
-                cur = cur->children;
-                continue;
+            if (cur->children != NULL) {
+                /* Always validate cur->parent when descending. */
+                if (cur->parent == parent) {
+                    parent = cur;
+                    cur = cur->children;
+                    continue;
+                }
+            } else {
+                xmlOutputBufferWriteString(buf, "\n");
             }
             break;
 
d/linux-boot.scm'>log</a><a href='/guix/tree/gnu/build/linux-boot.scm?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98'>tree</a><a href='/guix/commit/gnu/build/linux-boot.scm?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98'>commit</a><a href='/guix/diff/gnu/build/linux-boot.scm?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/build/linux-boot.scm'>
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<div class='path'>path: <a href='/guix/log/?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98'>root</a>/<a href='/guix/log/gnu?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98'>gnu</a>/<a href='/guix/log/gnu/build?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98'>build</a>/<a href='/guix/log/gnu/build/linux-boot.scm?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98'>linux-boot.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/build/linux-boot.scm?id=046d6d9f8e5456d651cdc69b04dfae3af5230a98&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-11-19 01:00:00 +0100'>2023-11-19</span></td><td><a href='/guix/commit/gnu/build/linux-boot.scm?id=d553249f7296b6e5807be75beb258dc82e86e928'>linux-boot: Don't create /root before it's used.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/linux-boot.scm (boot-system): Postpone the MKDIR of /root.

Change-Id: I589316a5ddf41cada02173ed4dd5b7df09b795e8
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2022-09-04 02:00:00 +0200'>2022-09-04</span></td><td><a href='/guix/commit/gnu/build/linux-boot.scm?id=ec16f88522041dc285a35705ff9ee95672b78143'>linux-boot: Resume from hibernation after pre-boot.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/linux-boot.scm (boot-system): Call resume-if-hibernated
after pre-mount.

Signed-off-by: Tobias Geerinckx-Rice &lt;me@tobias.gr&gt;
</span></span></td><td>Jack Hill</td></tr>
<tr><td><span title='2022-03-01 10:30:18 -0500'>2022-03-01</span></td><td><a href='/guix/commit/gnu/build/linux-boot.scm?id=6d9d616113cf051d80567b584a5b0a6489ddc065'>initrd: Honor rootfstype and rootflags command-line parameters.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/linux-boot.scm (boot-system): Honor rootfstype and rootflags
arguments.  Update doc.  Error out in case there is insufficient information
with regard to the root file system.
Restore the behavior of inferring the root device from the root file system
from the operating system in case the root argument is not provided.
* doc/guix.texi (Initial RAM Disk): Document the new command-line parameters.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-03-01 10:30:17 -0500'>2022-03-01</span></td><td><a href='/guix/commit/gnu/build/linux-boot.scm?id=0dc019e19a23fea614be5623360849ab9bc35e74'>initrd: Use non-hyphenated kernel command-line parameter names.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is to make it less surprising, given the common convention sets forth by
the kernel Linux command-line parameters.

* gnu/build/linux-boot.scm (boot-system): Rename '--load', '--repl', '--root'
and '--system' to 'gnu.load', 'gnu.repl', 'root' and 'gnu.system',
respectively.  Adjust doc.
(find-long-option): Adjust doc.
* gnu/installer/parted.scm (installer-root-partition-path): Adjust accordingly.
* gnu/system.scm (bootable-kernel-arguments): Add a VERSION argument and
update doc.  Use VERSION to conditionally return old style vs new style initrd
arguments.
(%boot-parameters-version): Increment to 1.
(operating-system-boot-parameters): Adjust doc.
(operating-system-boot-parameters-file): Likewise.
* gnu/system/linux-initrd.scm (raw-initrd, base-initrd): Likewise.
* doc/guix.texi: Adjust doc.
* gnu/build/activation.scm (boot-time-system): Adjust accordingly.
* gnu/build/hurd-boot.scm (boot-hurd-system): Likewise.
* gnu/packages/commencement.scm (%final-inputs-riscv64): Adjust comment.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-02-17 13:39:02 -0500'>2022-02-17</span></td><td><a href='/guix/commit/gnu/build/linux-boot.scm?id=e9f9f291edafaa27fa6d7e9967909555a08d383e'>build: linux-boot: Expound docstring of the 'boot-system' procedure.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/linux-boot.scm (boot-system): Document the Linux command-line
parameters it understands and split a long string over two lines.
</span></span></td><td>Maxim Cournoyer</td></tr>