MT#62750 media_player: skip MP init if there is ongoing MoH

Both the play media and the music on hold use
the `media_player::call_play_media_for_ml()` as an entrance
towards the `media_player::media_player_new()` and
`media_player::media_player_play_init()`.

Prevent allocation of new MoH over ongoing one,
as well as the `play media` command over ongoing MoH.

Otherwise a media player will be re-used to override
ongoing activity.

Explicit policy must be used:
First the MoH has to be stopped
by getting back to the SDP `sendrecv` state, before
any other MoH request, or play media request can be fulfilled.

Change-Id: Ia5fdc10cfa8f491109ade9a2225b182ccdaa4778

daemon/media_player.c

@@ -1706,9 +1706,17 @@ const char * call_play_media_for_ml(struct call_monologue *ml,
 
 	/* this starts the audio player if needed */
 	update_init_monologue_subscribers(ml, OP_PLAY_MEDIA);
-	/* media_player_new() now knows that audio player is in use
-	 * TODO: player options can have changed if already exists */
-	media_player_new(&ml->player, ml, NULL, &opts);
+
+	if (ml->player && ml->player->opts.moh) {
+		ilog(LOG_DEBUG, "There is already ongoing media playback for MoH. Ignore new one.");
+		/* pretend that everything is good */
+		return NULL;
+	}
+	else {
+		/* media_player_new() now knows that audio player is in use
+		* TODO: player options can have changed if already exists */
+		media_player_new(&ml->player, ml, NULL, &opts);
+	}
 
 	if (opts.file.len) {
 		if (!media_player_play_file(ml->player, opts))