Fix CVE-2016-5652 (buffer overflow in t2p_readwrite_pdf_image_tile()).

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-5652

Patches exfiltrated from upstream CVS repo with:
cvs diff -u -r 1.92 -r 1.94 tools/tiff2pdf.c

Index: tools/tiff2pdf.c
===================================================================
RCS file: /cvs/maptools/cvsroot/libtiff/tools/tiff2pdf.c,v
retrieving revision 1.92
retrieving revision 1.94
diff -u -r1.92 -r1.94
--- a/tools/tiff2pdf.c	23 Sep 2016 22:12:18 -0000	1.92
+++ b/tools/tiff2pdf.c	9 Oct 2016 11:03:36 -0000	1.94
@@ -2887,21 +2887,24 @@
 				return(0);
 			}
 			if(TIFFGetField(input, TIFFTAG_JPEGTABLES, &count, &jpt) != 0) {
-				if (count > 0) {
-					_TIFFmemcpy(buffer, jpt, count);
+				if (count >= 4) {
+                    /* Ignore EOI marker of JpegTables */
+					_TIFFmemcpy(buffer, jpt, count - 2);
 					bufferoffset += count - 2;
+                    /* Store last 2 bytes of the JpegTables */
 					table_end[0] = buffer[bufferoffset-2];
 					table_end[1] = buffer[bufferoffset-1];
-				}
-				if (count > 0) {
 					xuint32 = bufferoffset;
+                    bufferoffset -= 2;
 					bufferoffset += TIFFReadRawTile(
 						input, 
 						tile, 
-						(tdata_t) &(((unsigned char*)buffer)[bufferoffset-2]), 
+						(tdata_t) &(((unsigned char*)buffer)[bufferoffset]), 
 						-1);
-						buffer[xuint32-2]=table_end[0];
-						buffer[xuint32-1]=table_end[1];
+                    /* Overwrite SOI marker of image scan with previously */
+                    /* saved end of JpegTables */
+					buffer[xuint32-2]=table_end[0];
+					buffer[xuint32-1]=table_end[1];
 				} else {
 					bufferoffset += TIFFReadRawTile(
 						input,