dvbsubdec: add missing break

Fix a memory leak too.

CC: libav-stable@libav.org
Bug-Id: CID 732230

libavcodec/dvbsubdec.c

@@ -1444,6 +1444,7 @@ static int dvbsub_decode(AVCodecContext *avctx,
                 break;
             case DVBSUB_DISPLAYDEFINITION_SEGMENT:
                 dvbsub_parse_display_definition_segment(avctx, p, segment_length);
+                break;
             case DVBSUB_DISPLAY_SEGMENT:
                 *data_size = dvbsub_display_end_segment(avctx, p, segment_length, sub);
                 break;