Shortcircuit for -Su when target list is empty

The "Resolving dependencies... Please wait" message is displayed when target
list is empty for the -Su option. In addition, there is unnecessary changing
of directories and creation of data structures. Remove these when the target
list is empty.

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>

sync.c

@@ -482,6 +482,10 @@ static int upgrade_pkgs(alpm_list_t *targets, struct pw_hashdb *hashdb)
 	int ret = 0;
 
 	char cwd[PATH_MAX];
+	if (!targets) {
+		return 0;
+	}
+
 	if (!getcwd(cwd, PATH_MAX)) {
 		return error(PW_ERR_GETCWD);
 	}