Fix CVE-2016-5314.

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-5314
bugzilla.maptools.org/show_bug.cgi?id=2554

Patch extracted from upstream CVS repo with:
$ cvs diff -u -r1.43 -r1.44 libtiff/tif_pixarlog.c

Index: libtiff/tif_pixarlog.c
===================================================================
RCS file: /cvs/maptools/cvsroot/libtiff/libtiff/tif_pixarlog.c,v
retrieving revision 1.43
retrieving revision 1.44
diff -u -r1.43 -r1.44
--- libtiff/libtiff/tif_pixarlog.c	27 Dec 2015 20:14:11 -0000	1.43
+++ libtiff/libtiff/tif_pixarlog.c	28 Jun 2016 15:12:19 -0000	1.44
@@ -459,6 +459,7 @@
 typedef	struct {
 	TIFFPredictorState	predict;
 	z_stream		stream;
+	tmsize_t		tbuf_size; /* only set/used on reading for now */
 	uint16			*tbuf; 
 	uint16			stride;
 	int			state;
@@ -694,6 +695,7 @@
 	sp->tbuf = (uint16 *) _TIFFmalloc(tbuf_size);
 	if (sp->tbuf == NULL)
 		return (0);
+	sp->tbuf_size = tbuf_size;
 	if (sp->user_datafmt == PIXARLOGDATAFMT_UNKNOWN)
 		sp->user_datafmt = PixarLogGuessDataFmt(td);
 	if (sp->user_datafmt == PIXARLOGDATAFMT_UNKNOWN) {
@@ -783,6 +785,12 @@
 		TIFFErrorExt(tif->tif_clientdata, module, "ZLib cannot deal with buffers this size");
 		return (0);
 	}
+	/* Check that we will not fill more than what was allocated */
+	if (sp->stream.avail_out > sp->tbuf_size)
+	{
+		TIFFErrorExt(tif->tif_clientdata, module, "sp->stream.avail_out > sp->tbuf_size");
+		return (0);
+	}
 	do {
 		int state = inflate(&sp->stream, Z_PARTIAL_FLUSH);
 		if (state == Z_STREAM_END) {