Fix CVE-2018-6942:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-6942
https://people.canonical.com/~ubuntu-security/cve/2018/CVE-2018-6942.html

Copied from upstream (ChangeLog section removed):
https://git.savannah.gnu.org/cgit/freetype/freetype2.git/commit/?id=29c759284e305ec428703c9a5831d0b1fc3497ef

diff --git a/src/truetype/ttinterp.c b/src/truetype/ttinterp.c
index d855aaa..551f14a 100644
--- a/src/truetype/ttinterp.c
+++ b/src/truetype/ttinterp.c
@@ -7532,8 +7532,16 @@
       return;
     }
 
-    for ( i = 0; i < num_axes; i++ )
-      args[i] = coords[i] >> 2; /* convert 16.16 to 2.14 format */
+    if ( coords )
+    {
+      for ( i = 0; i < num_axes; i++ )
+        args[i] = coords[i] >> 2; /* convert 16.16 to 2.14 format */
+    }
+    else
+    {
+      for ( i = 0; i < num_axes; i++ )
+        args[i] = 0;
+    }
   }
 
 
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<tr><td><span title='2019-06-07 21:50:18 +0200'>2019-06-07</span></td><td><a href='/guix/commit/gnu/build/locale.scm?id=0e6cee21a48294b81a5e57e00602728fe7f7075f'>gnu: glibc-locales: Install symlinks using the normalized codeset.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/36076&gt;.
Reported by Jack Hill &lt;jackhill@jackhill.us&gt;
and Giovanni Biscuolo &lt;g@xelera.eu&gt;

* gnu/build/locale.scm (locale-&gt;name+codeset): New file.
* gnu/packages/base.scm (make-glibc-locales): Add #:modules
and #:imported-modules.  Add a 'symlink-normalized-codesets' phase.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-06-07 21:50:18 +0200'>2019-06-07</span></td><td><a href='/guix/commit/gnu/build/locale.scm?id=15ec93a7832ae7dde747ccd9bb2bb2776be9f199'>Add (gnu build locale).</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/locale.scm: New file.
* gnu/local.mk (MODULES_NOT_COMPILED): Add it.
* gnu/installer/locale.scm (normalize-codeset): Remove.
* gnu/system/locale.scm (localedef-command): Remove.
(single-locale-directory): Use (gnu build locale).
(glibc-supported-locales)[build]: Likewise, and remove
'read-supported-locales'.
</span></span></td><td>Ludovic Courtès</td></tr>