fix: Fix hook useLocaleMessages to accept fallback locales.

[GuiLeme]

What does this PR do?

it fixes the locale fallback for our useLocaleMessages hook

Motivation

Previously, if the localeUrl was not accessible, the hook would send the previous locale selected as default (so if I am changing from pt-BR -> fr, the locales would still be pt-BR instead of en which is usually the fallback)

More

No PRs from CORE is needed.

See demo below:

1. Locale is en;
2. Change locale to pt-BR (which is already complete for pick-random-user);
3. Change locale to fr (which is mocked to not be complete);
4. See that the labels that does exist are there in French, and the ones that doesn't, are in English (current behaviour of BBB-core);

useLocaleMessagesFallbackFix.mp4