[45]region: Prevent crash of accessing invalid pointer

In !2051 (merged), we switch back to real locale before setting the label text, however, according to nl_langinfo's manpage, the returned pointer could be invalid after switching locale or creating new locale, so the program may crash.

To fix this, we save the result before switching locale, so we won't access the invalid pointer after switching locale.

This is a backport of !2121 (merged) for gnome-45 branch.