Fix divide-by-zero in OJPEGDecodeRaw():

http://bugzilla.maptools.org/show_bug.cgi?id=2611

2016-12-03 Even Rouault <even.rouault at spatialys.com>

        * libtiff/tif_ojpeg.c: make OJPEGDecode() early exit in case of failure
in
        OJPEGPreDecode(). This will avoid a divide by zero, and potential other
issues.
        Reported by Agostino Sarubbo.
        Fixes http://bugzilla.maptools.org/show_bug.cgi?id=2611

/cvs/maptools/cvsroot/libtiff/ChangeLog,v  <--  ChangeLog
new revision: 1.1177; previous revision: 1.1176
/cvs/maptools/cvsroot/libtiff/libtiff/tif_ojpeg.c,v  <--  libtiff/tif_ojpeg.c
new revision: 1.66; previous revision: 1.65

Index: libtiff/libtiff/tif_ojpeg.c
===================================================================
RCS file: /cvs/maptools/cvsroot/libtiff/libtiff/tif_ojpeg.c,v
retrieving revision 1.65
retrieving revision 1.66
diff -u -r1.65 -r1.66
--- libtiff/libtiff/tif_ojpeg.c	4 Sep 2016 21:32:56 -0000	1.65
+++ libtiff/libtiff/tif_ojpeg.c	3 Dec 2016 11:15:18 -0000	1.66
@@ -1,4 +1,4 @@
-/* $Id: tif_ojpeg.c,v 1.65 2016-09-04 21:32:56 erouault Exp $ */
+/* $Id: tif_ojpeg.c,v 1.66 2016-12-03 11:15:18 erouault Exp $ */
 
 /* WARNING: The type of JPEG encapsulation defined by the TIFF Version 6.0
    specification is now totally obsolete and deprecated for new applications and
@@ -244,6 +244,7 @@
 
 typedef struct {
 	TIFF* tif;
+        int decoder_ok;
 	#ifndef LIBJPEG_ENCAP_EXTERNAL
 	JMP_BUF exit_jmpbuf;
 	#endif
@@ -722,6 +723,7 @@
 		}
 		sp->write_curstrile++;
 	}
+	sp->decoder_ok = 1;
 	return(1);
 }
 
@@ -784,8 +786,14 @@
 static int
 OJPEGDecode(TIFF* tif, uint8* buf, tmsize_t cc, uint16 s)
 {
+        static const char module[]="OJPEGDecode";
 	OJPEGState* sp=(OJPEGState*)tif->tif_data;
 	(void)s;
+        if( !sp->decoder_ok )
+        {
+            TIFFErrorExt(tif->tif_clientdata,module,"Cannot decode: decoder not correctly initialized");
+            return 0;
+        }
 	if (sp->libjpeg_jpeg_query_style==0)
 	{
 		if (OJPEGDecodeRaw(tif,buf,cc)==0)