ww8: make sure we don't wrap around

Change-Id: I667bb264f92024b72f230c2ddbba3887471345f2
(cherry picked from commit 755b9320)

sw/source/filter/ww8/ww8scan.cxx

@@ -1542,7 +1542,11 @@ WW8PLCFpcd* WW8ScannerBase::OpenPieceTable( SvStream* pStr, const WW8Fib* pWwF )
         if( 2 == clxt )                         // PLCFfpcd ?
             break;                              // PLCFfpcd gefunden
         if( 1 == clxt )                         // clxtGrpprl ?
+        {
+            if (nGrpprl == SHRT_MAX)
+                return NULL;
             nGrpprl++;
+        }
         sal_uInt16 nLen(0);
         pStr->ReadUInt16( nLen );
         nLeft -= 2 + nLen;