compositor: change position of weston_log_file_open call

In case XDG_RUNTIME_DIR was not set, weston_log
will crash the compositor instead of spitting
error msg, as weston log was not yet opened

src/compositor.c

@@ -3170,13 +3170,13 @@ int main(int argc, char *argv[])
 	argc = parse_options(core_options,
 			     ARRAY_LENGTH(core_options), argc, argv);
 
+	weston_log_file_open(log);
+	
 	if (!getenv("XDG_RUNTIME_DIR")) {
 		weston_log(xdg_error_message);
 		exit(EXIT_FAILURE);
 	}
 
-	weston_log_file_open(log);
-
 	gettimeofday(&tv, NULL);
 	brokendown_time = localtime(&tv.tv_sec);
 	strftime(buffer, sizeof buffer, "%Y-%m-%d %H:%M:%S", brokendown_time);