avcodec/anm: fix palette alpha

Signed-off-by: Marton Balint <cus@passwd.hu>

libavcodec/anm.c

@@ -54,7 +54,7 @@ static av_cold int decode_init(AVCodecContext *avctx)
 
     bytestream2_skipu(&s->gb, 16 * 8);
     for (i = 0; i < 256; i++)
-        s->palette[i] = bytestream2_get_le32u(&s->gb);
+        s->palette[i] = (0xFFU << 24) | bytestream2_get_le32u(&s->gb);
 
     return 0;
 }