vl/mpeg12: make bitstream decoder more robust

Just another xine workaround.

Signed-off-by: Christian König <deathsimple@vodafone.de>

src/gallium/auxiliary/vl/vl_mpeg12_bitstream.c

@@ -825,6 +825,8 @@ decode_slice(struct vl_mpg12_bs *bs, struct pipe_video_buffer *target)
       }
       inc += vl_vlc_get_vlclbf(&bs->vlc, tbl_B1, 11);
       if (x != -1) {
+         if (!inc)
+            return;
          mb.num_skipped_macroblocks = inc - 1;
          bs->decoder->decode_macroblock(bs->decoder, target, &bs->desc->base, &mb.base, 1);
       }

src/gallium/auxiliary/vl/vl_vlc.h

@@ -271,7 +271,6 @@ vl_vlc_get_vlclbf(struct vl_vlc *vlc, const struct vl_vlc_entry *tbl, unsigned n
 {
    tbl += vl_vlc_peekbits(vlc, num_bits);
    vl_vlc_eatbits(vlc, tbl->length);
-   assert(tbl->length);
    return tbl->value;
 }