Fixes switch_locale not adding locale if missing from URL

[Quirinus]

If the language code was missing in the URI, switch_locale(locale) didn't add it (it worked fine if it was present). That means that it produced the same URL for all locales, each missing the language code in the URL.

Description

I added an additional check that checks if the language is set in the URI, and it is changed only in that case. Otherwise if it was missing, it was producing a URL that doesn't contain it - but now it does add the launguage code to the URL if it was missing.

Motivation and Context

Fixes #870

Screenshots (if appropriate):

Notice the current URL for a collection named "test" (not containing any language code in the URL). I hovered the mouse over the link to change the locale to "hr" (top right), and the URL that is in that link is shown on bottom left - it doesn't contain "hr". Same happens when I hover over "en".

Types of changes

• [ ] Replay fix (fixes a replay specific issue)
• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added or updated tests to cover my changes.
• [ ] All new and existing tests passed.

I don't know how to run the tests.

[Quirinus]

I tested this using the default web server ("wayback" command). Hopefully it works well with uwsgi too.

I will check if I have time.