avcodec/vc1_block: Check for end of bitstream at the top of vc1_decode_i_blocks_adv()

Fixes: Timeout (147sec -> 2sec)
Fixes: 17704/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VC1IMAGE_fuzzer-5723851098423296

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/vc1_block.c

@@ -2661,7 +2661,7 @@ static void vc1_decode_i_blocks(VC1Context *v)
 
 /** Decode blocks of I-frame for advanced profile
  */
-static void vc1_decode_i_blocks_adv(VC1Context *v)
+static int vc1_decode_i_blocks_adv(VC1Context *v)
 {
     int k;
     MpegEncContext *s = &v->s;
@@ -2672,6 +2672,9 @@ static void vc1_decode_i_blocks_adv(VC1Context *v)
     int mqdiff;
     GetBitContext *gb = &s->gb;
 
+    if (get_bits_left(gb) <= 1)
+        return AVERROR_INVALIDDATA;
+
     /* select coding mode used for VLC tables selection */
     switch (v->y_ac_table_index) {
     case 0:
@@ -2775,7 +2778,7 @@ static void vc1_decode_i_blocks_adv(VC1Context *v)
                 ff_er_add_slice(&s->er, 0, s->start_mb_y, s->mb_x, s->mb_y, ER_MB_ERROR);
                 av_log(s->avctx, AV_LOG_ERROR, "Bits overconsumption: %i > %i\n",
                        get_bits_count(&s->gb), v->bits);
-                return;
+                return 0;
             }
             inc_blk_idx(v->topleft_blk_idx);
             inc_blk_idx(v->top_blk_idx);
@@ -2793,6 +2796,7 @@ static void vc1_decode_i_blocks_adv(VC1Context *v)
         ff_mpeg_draw_horiz_band(s, (s->end_mb_y - 1) * 16, 16);
     ff_er_add_slice(&s->er, 0, s->start_mb_y << v->field_mode, s->mb_width - 1,
                     (s->end_mb_y << v->field_mode) - 1, ER_MB_END);
+    return 0;
 }
 
 static void vc1_decode_p_blocks(VC1Context *v)