avcodec/cavsdec: Check bits left before picture allocation

Fixes: Timeout
Fixes: 57893/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_CAVS_fuzzer-5091726540013568

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

libavcodec/cavsdec.c

@@ -1020,6 +1020,9 @@ static int decode_pic(AVSContext *h)
             skip_bits(&h->gb, 1); //marker_bit
     }
 
+    if (get_bits_left(&h->gb) < 23)
+        return AVERROR_INVALIDDATA;
+
     ret = ff_get_buffer(h->avctx, h->cur.f, h->cur.f->pict_type == AV_PICTURE_TYPE_B ?
                         0 : AV_GET_BUFFER_FLAG_REF);
     if (ret < 0)