Fix CVE-2016-3623.

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-3623
http://bugzilla.maptools.org/show_bug.cgi?id=2569

Patch extracted from upstream CVS repo with:
$ cvs diff -u -r1.16 -r1.17 tools/rgb2ycbcr.c

Index: tools/rgb2ycbcr.c
===================================================================
RCS file: /cvs/maptools/cvsroot/libtiff/tools/rgb2ycbcr.c,v
retrieving revision 1.16
retrieving revision 1.17
diff -u -r1.16 -r1.17
--- libtiff/tools/rgb2ycbcr.c	21 Jun 2015 01:09:10 -0000	1.16
+++ libtiff/tools/rgb2ycbcr.c	15 Aug 2016 21:26:56 -0000	1.17
@@ -95,9 +95,13 @@
 			break;
 		case 'h':
 			horizSubSampling = atoi(optarg);
+            if( horizSubSampling != 1 && horizSubSampling != 2 && horizSubSampling != 4 )
+                usage(-1);
 			break;
 		case 'v':
 			vertSubSampling = atoi(optarg);
+            if( vertSubSampling != 1 && vertSubSampling != 2 && vertSubSampling != 4 )
+                usage(-1);
 			break;
 		case 'r':
 			rowsperstrip = atoi(optarg);
s='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=bde70b152575da0a3b87b7e26c46a5eec02694cb'>refs</a><a class='active' href='/guix/log/tests/networking.scm'>log</a><a href='/guix/tree/tests/networking.scm?id=bde70b152575da0a3b87b7e26c46a5eec02694cb'>tree</a><a href='/guix/commit/tests/networking.scm?id=bde70b152575da0a3b87b7e26c46a5eec02694cb'>commit</a><a href='/guix/diff/tests/networking.scm?id=bde70b152575da0a3b87b7e26c46a5eec02694cb'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/networking.scm'>
<input type='hidden' name='id' value='bde70b152575da0a3b87b7e26c46a5eec02694cb'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=bde70b152575da0a3b87b7e26c46a5eec02694cb'>root</a>/<a href='/guix/log/tests?id=bde70b152575da0a3b87b7e26c46a5eec02694cb'>tests</a>/<a href='/guix/log/tests/networking.scm?id=bde70b152575da0a3b87b7e26c46a5eec02694cb'>networking.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/tests/networking.scm?id=bde70b152575da0a3b87b7e26c46a5eec02694cb&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-04-07 17:56:07 +0200'>2023-04-07</span></td><td><a href='/guix/commit/tests/networking.scm?id=b92880d0118d3a89a879515f8d373d5dbd281cf9'>services: ntp-service-type: Remove deprecated server as strings support.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/networking.scm (&lt;ntp-configuration&gt;)[servers]: Rename accessor to ntp-configuration-servers.
(ntp-configuration-servers): Remove helper procedure.
(ntp-shepherd-service): Remove helper procedure usage.
* tests/networking.scm: Remove obsolete test.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Bruno Victal</td></tr>