bmp image: check for out of range image size.

Make the decoder fail early to avoid spending time and memory on
attempting to decode a corrupt image file.

Based on Qt5 patch for CVE-2018-19873.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>

src/kernel/qimage.cpp

@@ -4667,6 +4667,8 @@ bool read_dib( TQDataStream& s, int offset, int startpos, TQImage& image )
     if ( !(comp == BMP_RGB || (nbits == 4 && comp == BMP_RLE4) ||
 	(nbits == 8 && comp == BMP_RLE8) || ((nbits == 16 || nbits == 32) && comp == BMP_BITFIELDS)) )
 	 return FALSE;				// weird compression type
+    if ((w < 0) || ((w * abs(h)) > (16384 * 16384)))
+        return FALSE;
 
     int ncols;
     int depth;