h264: try to better handle h264 streams that are slightly truncated

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

libavcodec/h264.c

@@ -4032,7 +4032,7 @@ static int decode_slice(struct AVCodecContext *avctx, void *arg)
                     loop_filter(h, lf_x_start, s->mb_x + 1);
                 return 0;
             }
-            if (ret < 0 || h->cabac.bytestream > h->cabac.bytestream_end + 2) {
+            if (ret < 0 || h->cabac.bytestream > h->cabac.bytestream_end + 4) {
                 av_log(h->s.avctx, AV_LOG_ERROR,
                        "error while decoding MB %d %d, bytestream (%td)\n",
                        s->mb_x, s->mb_y,