sws: dont write out of array on bigendian

Fixes Ticket2229

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 4e2c63685e)

libswscale/swscale_unscaled.c

@@ -483,6 +483,9 @@ static rgbConvFn findRgbConvFn(SwsContext *c)
         }
     }
 
+    if ((dstFormat == PIX_FMT_RGB32_1 || dstFormat == PIX_FMT_BGR32_1) && !isRGBA32(srcFormat) && ALT32_CORR<0)
+        return NULL;
+
     return conv;
 }