avcodec/msvideo1: Fix palette in case of seek before decode

Fixes Ticket3212
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/msvideo1.c

@@ -67,6 +67,8 @@ static av_cold int msvideo1_decode_init(AVCodecContext *avctx)
     if (s->avctx->bits_per_coded_sample == 8) {
         s->mode_8bit = 1;
         avctx->pix_fmt = AV_PIX_FMT_PAL8;
+        if (avctx->extradata_size >= AVPALETTE_SIZE)
+            memcpy(s->pal, avctx->extradata, AVPALETTE_SIZE);
     } else {
         s->mode_8bit = 0;
         avctx->pix_fmt = AV_PIX_FMT_RGB555;