Fix condition for transparency warning in xsub encoder.

libavcodec/xsubenc.c

@@ -142,7 +142,7 @@ static int xsub_encode(AVCodecContext *avctx, unsigned char *buf,
         av_log(avctx, AV_LOG_WARNING, "No more than 4 subtitle colors supported (%d found.)\n", h->rects[0]->nb_colors);
 
     // TODO: Palette swapping if color zero is not transparent
-    if (((uint32_t *)h->rects[0]->pict.data[1])[0] & 0xff)
+    if (((uint32_t *)h->rects[0]->pict.data[1])[0] & 0xff000000)
         av_log(avctx, AV_LOG_WARNING, "Color index 0 is not transparent. Transparency will be messed up.\n");
 
     if (make_tc(startTime, start_tc) || make_tc(endTime, end_tc)) {