fix misc memory leaks

This fixes a few misc memory leaks reported by asan:
- Items of `config->config_chain` are now freed instead of just the list
itself
- `bar->swaybar_command` is now freed
- The result returned by a seat subcommand is now returned instead of
leaked

sway/commands/seat.c

@@ -50,5 +50,5 @@ struct cmd_results *cmd_seat(int argc, char **argv) {
 	}
 
 	config->handler_context.seat_config = NULL;
-	return cmd_results_new(CMD_SUCCESS, NULL);
+	return res ? res : cmd_results_new(CMD_SUCCESS, NULL);
 }