Don't show window until file is loaded

[Keithcat1]

For large files, showing the window while loading can cause NVDA to become unresponsive for several seconds.

[trypsynth]

Thanks for this, although I'm sorry to say this is not the approach I had in mind. This is why I like people to open issues before making changes like this, but we can always move over to a discussion if necessary. My ideal UX would be a loading dialog that shows up for only like 200 ms if yo uload a teeny book, a few seconds if you load a giant one, or a tad longer if you're loading multiple documents. Importantly, it should not flash for every document opened, it shouldn't give you verbose speech, just something like "loading, dialog", etc.