When new streams are detected, look for old filters and close them out.

This avoids crashes seen when legitimate streams are found on PID 0x11 instead
of DVB SDT.
Fixes regression detailed in Roundup issue 138.

Originally committed as revision 11050 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mpegts.c

@@ -588,11 +588,11 @@ static void pmt_cb(MpegTSFilter *filter, const uint8_t *section, int section_len
         case STREAM_TYPE_AUDIO_AC3:
         case STREAM_TYPE_AUDIO_DTS:
         case STREAM_TYPE_SUBTITLE_DVB:
-            if(ts->pids[pid]){
-                assert(ts->pids[pid]->type == MPEGTS_PES);
+            if(ts->pids[pid] && ts->pids[pid]->type == MPEGTS_PES){
                 pes= ts->pids[pid]->u.pes_filter.opaque;
                 st= pes->st;
             }else{
+                if (ts->pids[pid]) mpegts_close_filter(ts, ts->pids[pid]); //wrongly added sdt filter probably
                 pes = add_pes_stream(ts, pid, pcr_pid, stream_type);
                 if (pes)
                     st = new_pes_av_stream(pes, 0);