avcodec/microdvddec: add some memory checks

libavcodec/microdvddec.c

@@ -261,7 +261,6 @@ static int microdvd_decode_frame(AVCodecContext *avctx,
     AVSubtitle *sub = data;
     AVBPrint new_line;
     char c;
-    char *decoded_sub;
     char *line = avpkt->data;
     char *end = avpkt->data + avpkt->size;
     struct microdvd_tag tags[sizeof(MICRODVD_TAGS) - 1] = {{0}};
@@ -301,18 +300,18 @@ static int microdvd_decode_frame(AVCodecContext *avctx,
         }
     }
     if (new_line.len) {
-        av_bprintf(&new_line, "\r\n");
-
-        av_bprint_finalize(&new_line, &decoded_sub);
-        if (*decoded_sub) {
+        int ret;
             int64_t start    = avpkt->pts;
             int64_t duration = avpkt->duration;
             int ts_start     = av_rescale_q(start,    avctx->time_base, (AVRational){1,100});
             int ts_duration  = duration != -1 ?
                 av_rescale_q(duration, avctx->time_base, (AVRational){1,100}) : -1;
-            ff_ass_add_rect(sub, decoded_sub, ts_start, ts_duration, 0);
-        }
-        av_free(decoded_sub);
+
+        av_bprintf(&new_line, "\r\n");
+        ret = ff_ass_add_rect_bprint(sub, &new_line, ts_start, ts_duration, 0);
+        av_bprint_finalize(&new_line, NULL);
+        if (ret < 0)
+            return ret;
     }
 
     *got_sub_ptr = sub->num_rects > 0;