Do not allow tab closure during upload

What is the problem you are facing?

Sometimes I don't pay attention to the fact that I'm uploading in the background and might close the tab open on Funkwhale and so losing any upload progress. It might be nice to have a pop-up with remember the choice etc to ask if we really want to close the tab during upload.

What are the possible drawbacks or issues with the requested changes?

I don't know.