lavfi/vf_ass: ignore subtitles decoding errors.

A broken packet with invalid data in the middle of the stream
should not prevent from decoding the rest of the file.

Work around trac ticket #2264.

libavfilter/vf_ass.c

@@ -318,14 +318,18 @@ static av_cold int init_subtitles(AVFilterContext *ctx, const char *args)
 
         if (pkt.stream_index == sid) {
             ret = avcodec_decode_subtitle2(dec_ctx, &sub, &got_subtitle, &pkt);
-            if (ret < 0 || !got_subtitle)
-                break;
+            if (ret < 0) {
+                av_log(ctx, AV_LOG_WARNING, "Error decoding: %s (ignored)\n",
+                       av_err2str(ret));
+            } else if (got_subtitle) {
+                /* TODO reindent */
             for (i = 0; i < sub.num_rects; i++) {
                 char *ass_line = sub.rects[i]->ass;
                 if (!ass_line)
                     break;
                 ass_process_data(ass->track, ass_line, strlen(ass_line));
             }
+            }
         }
         av_free_packet(&pkt);
         avsubtitle_free(&sub);