Fix long filenames missing . in extension

[bunny-foofoo]

Fix for #753

Long file names which end with . were having their path broken during shortening.
e.g.; would be saved as ../../shortened_filenamemp4 instead of ../../shortened_filename.mp4

Fixed the issue and added test coverage for this case.

[OMEGARAZER]

This commit fixes the broken test afd2f88

[Serene-Arc]

You a maintainer now @OMEGARAZER ?

[OMEGARAZER]

If you mean the approve, it was twofold.

1. I saw the button and wanted to see if it worked or gave me an error and

2. If no error, to say that I tried out the changes in this PR and they all worked and passed.

But as far as I'm aware I'm not, no.

[Serene-Arc]

All good, just need to know how the permissions distribution. If all the tests passed, then I can merge it