Fix a integer underflow in tiffcp that led to heap overflows in
TIFFReverseBits():

http://bugzilla.maptools.org/show_bug.cgi?id=2598

2016-12-02 Even Rouault <even.rouault at spatialys.com>

        * tools/tiffcp.c: avoid uint32 underflow in cpDecodedStrips that 
        can cause various issues, such as buffer overflows in the library.
        Reported by Agostino Sarubbo.
        Fixes http://bugzilla.maptools.org/show_bug.cgi?id=2598


/cvs/maptools/cvsroot/libtiff/ChangeLog,v  <--  ChangeLog
new revision: 1.1174; previous revision: 1.1173
/cvs/maptools/cvsroot/libtiff/tools/tiffcp.c,v  <--  tools/tiffcp.c
new revision: 1.56; previous revision: 1.55

Index: libtiff/tools/tiffcp.c
===================================================================
RCS file: /cvs/maptools/cvsroot/libtiff/tools/tiffcp.c,v
retrieving revision 1.55
retrieving revision 1.56
diff -u -r1.55 -r1.56
--- libtiff/tools/tiffcp.c	8 Oct 2016 15:54:57 -0000	1.55
+++ libtiff/tools/tiffcp.c	2 Dec 2016 22:13:32 -0000	1.56
@@ -1,4 +1,4 @@
-/* $Id: tiffcp.c,v 1.55 2016-10-08 15:54:57 erouault Exp $ */
+/* $Id: tiffcp.c,v 1.56 2016-12-02 22:13:32 erouault Exp $ */
 
 /*
  * Copyright (c) 1988-1997 Sam Leffler
@@ -985,7 +985,7 @@
 		tstrip_t s, ns = TIFFNumberOfStrips(in);
 		uint32 row = 0;
 		_TIFFmemset(buf, 0, stripsize);
-		for (s = 0; s < ns; s++) {
+		for (s = 0; s < ns && row < imagelength; s++) {
 			tsize_t cc = (row + rowsperstrip > imagelength) ?
 			    TIFFVStripSize(in, imagelength - row) : stripsize;
 			if (TIFFReadEncodedStrip(in, s, buf, cc) < 0