fix transcoding reflector crash

eg. crashed: `hd-rum-transcode 8M 5004 -c lavc:c=H.264 -P 8000 ::1`

fec should not be set to nullptr (RXTX init sets "none" by default)

Author: MartinPulec

src/hd-rum-translator/hd-rum-recompress.cpp

@@ -129,7 +129,9 @@ recompress_output_port::recompress_output_port(
         params.receiver = this->host.c_str();
         params.medium[TX_MEDIA_VIDEO].rx_port = rx_port;
         params.medium[TX_MEDIA_VIDEO].tx_port = tx_port;
-        params.medium[TX_MEDIA_VIDEO].fec = fec;
+        if (fec != nullptr) {
+                params.medium[TX_MEDIA_VIDEO].fec = fec;
+        }
         params.video_bitrate_limit = bitrate;
 
         // UltraGrid RTP - fllowing already set by VRXTX_INIT

src/rxtx/rtp_common.c

@@ -309,6 +309,7 @@ init_medium_state(struct rtp_rxtx_common_priv_state *s,
                 { &video_offset, params->video_bitrate_limit,
                  MODULE_CLASS_VIDEO                                              },
         };
+        assert(params_medium->fec != nullptr);
         const char       *medium_str    = get_tx_name(t);
         volatile int     *medium_offset = medium_defaults[t].medium_offset;
         long long         bitrate_limit = medium_defaults[t].bitrate_limit;