command: print error message on "addid" failure

Returning the playlist_result value from a command handler does not
make sense.  Call print_playlist_result() there, and forward its
return value.

src/command.c

@@ -464,7 +464,7 @@ static int handleAddId(struct client *client,
 	enum playlist_result result = addToPlaylist(argv[1], &added_id);
 
 	if (result != PLAYLIST_RESULT_SUCCESS)
-		return result;
+		return print_playlist_result(client, result);
 
 	if (argc == 3) {
 		int to;