I have to go to bed because it's almost 3 a.m. here.
But...
When trying to open an EPUB file from the web, e.g.
https://github.com/Sigil-Ebook/Sigil...ork_rev15.epub, the file is first checked by the
Utility::IsFileReadable function, which prevents a crash.
I suspect that this allows us to use the native window without any problems if we add this check to the
BookBrowser::AddExisting() function as well.
I can only check it myself on Sunday, because tomorrow I have a day trip.