Fix security issue CVE-2015-0295

[taken from RedHat Qt3 patches]
(cherry picked from commit b3037160f2)

src/kernel/qimage.cpp

@@ -4716,10 +4716,16 @@ bool read_dib( QDataStream& s, int offset, int startpos, QImage& image )
 	if ( (Q_ULONG)d->readBlock( (char *)&blue_mask, sizeof(blue_mask) ) != sizeof(blue_mask) )
 	    return FALSE;
 	red_shift = calc_shift(red_mask);
+	if (((red_mask >> red_shift) + 1) == 0)
+	    return FALSE;
 	red_scale = 256 / ((red_mask >> red_shift) + 1);
 	green_shift = calc_shift(green_mask);
+	if (((green_mask >> green_shift) + 1) == 0)
+	    return FALSE;
 	green_scale = 256 / ((green_mask >> green_shift) + 1);
 	blue_shift = calc_shift(blue_mask);
+	if (((blue_mask >> blue_shift) + 1) == 0)
+	    return FALSE;
 	blue_scale = 256 / ((blue_mask >> blue_shift) + 1);
     } else if (comp == BMP_RGB && (nbits == 24 || nbits == 32)) {
 	blue_mask = 0x000000ff;