Fix security issue CVE-2015-1860

[taken from RedHat Qt3 patches]

src/kernel/qasyncimageio.cpp

@@ -1226,6 +1226,8 @@ void QGIFFormat::fillRect(QImage& img, int col, int row, int w, int h, QRgb colo
 
 void QGIFFormat::nextY(QImage& img, QImageConsumer* consumer)
 {
+    if (out_of_bounds)
+        return;
     int my;
     switch (interlace) {
       case 0: