fix issue with sort_language_hack returning None

[elfkuzco]

Rationale

When run with --languages flag, the scraper throws an error

 self.zim_languages = ",".join(
                         ^^^^^^^^^
TypeError: can only join an iterable

This is because the list.sort method returns None as it sorts the list in place.

            return list(languages).sort(
                key=lambda x: -1 if x == "eng" else 0
            )  # pyright: ignore[reportReturnType]

Changes

• Use the sorted function which returns a list instead rather than the list.sort which returns None.
• Check for the possibility that after sorting, the languages set might still be empty, in which case, set zim_language to eng

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 0.00%. Comparing base (d57d160) to head (de6ad9e).

Files	Patch %	Lines
src/ted2zim/scraper.py	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #175 +/- ## ===================================== Coverage 0.00% 0.00% ===================================== Files 7 7 Lines 1011 1011 Branches 215 215 ===================================== Misses 1011 1011 ```

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[elfkuzco]

Yes, it is okay.