check np bounds yet again

Change-Id: Id3f6fdc0ebed9711acec5d71f404e7a6072b765c
(cherry picked from commit bca4d6f8)
Reviewed-on: https://gerrit.libreoffice.org/17207Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>

filter/source/graphicfilter/itiff/itiff.cxx

@@ -669,6 +669,8 @@ bool TIFFReader::ReadMap()
                     pTIFF->Seek(pStripOffsets[nStrip]);
                 }
                 nRowBytesLeft = nBytesPerRow;
+                if (np >= SAL_N_ELEMENTS(pMap))
+                    return false;
                 pdst=pMap[ np ];
                 do
                 {