bmp image handler: 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.

Change-Id: I874e04f3b43122d73f8e58c7a5bcc4a741b68264
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/gui/image/qbmphandler.cpp

@@ -188,6 +188,8 @@ static bool read_dib_infoheader(QDataStream &s, BMP_INFOHDR &bi)
     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 (bi.biWidth < 0 || quint64(bi.biWidth) * qAbs(bi.biHeight) > 16384 * 16384)
+        return false;
 
     return true;
 }