region: don't crash for locales with no country_code

gnome_parse_locale() can return an empty country_code for some locales,
which we are not taking into account when building the simple_locale
string.

[endlessm/eos-shell#4017]
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[endlessm/eos-shell#4017]
Merge pull request #24 from endlessm/shell/4017

region: don't crash for locales with no country_code