locale-setup: do not load locale from environemnt when /etc/locale.conf is unchanged

Previously, when /etc/locale.conf is unchanged, locales were loaded from
possibly outdated environment variable.

Fixes a bug introduced by 018befc (v253).
Fixes #35717.

(cherry picked from commit 80797bb)
(cherry picked from commit d00cc09)
(cherry picked from commit d19d42b)
(cherry picked from commit 79b3378)
(cherry picked from commit f043ab6)

Author: yuwata

src/shared/locale-setup.c

@@ -75,7 +75,7 @@ static int locale_context_load_conf(LocaleContext *c, LocaleLoadFlag flag) {
 
         /* If the file is not changed, then we do not need to re-read the file. */
         if (stat_inode_unmodified(&c->st, &st))
-                return 0;
+                return 1; /* (already) loaded */
 
         c->st = st;
         locale_context_clear(c);