Check for errors from newlocale()
We accidentally deleted all locales from Fedora in yesterday's rawhide build. This revealed a bug in my uselocale changes to gnome-initial-setup: when a locale is missing from the system, g-i-s will crash rather than degrading gracefully. This is easy to fix, so let's do so.
We also ignore errors from uselocale(), but this is probably OK because the only possible error is passing in an invalid locale object, which is no longer possible after this commit.