Make MSS1 palette opaque.

libavcodec/mss1.c

@@ -554,7 +554,7 @@ static int decode_pal(MSS1Context *ctx, ArithCoder *acoder)
         r = arith_get_bits(acoder, 8);
         g = arith_get_bits(acoder, 8);
         b = arith_get_bits(acoder, 8);
-        *pal++ = (r << 16) | (g << 8) | b;
+        *pal++ = (0xFF << 24) | (r << 16) | (g << 8) | b;
     }
 
     return 0;
@@ -803,7 +803,7 @@ static av_cold int mss1_decode_init(AVCodecContext *avctx)
            av_int2float(AV_RB32(avctx->extradata + 44)));
 
     for (i = 0; i < 256; i++)
-        c->pal[i] = AV_RB24(avctx->extradata + 52 + i * 3);
+        c->pal[i] = 0xFF << 24 | AV_RB24(avctx->extradata + 52 + i * 3);
 
     avctx->pix_fmt = PIX_FMT_PAL8;