res_pjsip_session: Don't add declined stream if one does not exist.

Given a scenario where a session refresh was done with a removed
stream we would always add a removed stream to the outgoing SDP
even if one did not already exist.

This change makes it so that a removed stream is only placed into
the SDP if one already exists.

ASTERISK-28047

Change-Id: Ibb97d21cdeb87a8acae0c720861b0ff255708442

res/res_pjsip_session.c

@@ -1573,6 +1573,11 @@ int ast_sip_session_refresh(struct ast_sip_session *session,
 
 				/* No need to do anything with stream if it's media state is removed */
 				if (ast_stream_get_state(stream) == AST_STREAM_STATE_REMOVED) {
+					/* If there is no existing stream we can just not have this stream in the topology at all. */
+					if (!existing_stream) {
+						ast_stream_topology_del_stream(media_state->topology, index);
+						index -= 1;
+					}
 					continue;
 				}