assignment: clear codec when none was included

Change-Id: Ic2aea409c86bb1b0ee23200da597f5c8ef3aa2f1
diff --git a/src/libmsc/msc_a.c b/src/libmsc/msc_a.c
index 1078147..a6db397 100644
--- a/src/libmsc/msc_a.c
+++ b/src/libmsc/msc_a.c
@@ -1441,6 +1441,8 @@
 
 		/* Update codecs filter with the codec chosen by Assignment */
 		cc_trans->cc.codecs.assignment = m->sdp;
+	} else {
+		cc_trans->cc.codecs.assignment = (struct sdp_audio_codec){};
 	}
 	rtp_stream_set_remote_addr(rtps_to_ran, &ac->assignment_complete.remote_rtp);