Blank window when attempting to import deck

There have been a number of reports of the import screen going blank when importing an .apkg and clicking on the Import button. I've attempted to reproduce this with an .apkg provided by a user, but couldn't seem to trigger it. Maybe we'll have more luck with a different .apkg, a different user's collection to import into, or a different machine that is faster/slower.

Users who are experiencing this might be able to give us some insight into what's happening here by viewing the import screen in the web inspector. Right clicking when the screen goes blank, opening the inspector, and then opening the Console window may reveal an error.

Originally reported on https://forums.ankiweb.net/t/importing-file-does-not-work/46575 and other locations.

Start by reproducing the blank screen while importing an .apkg, trying the provided user file, different collections, and machines with different performance. Use the import screen's web inspector and Console to capture the error; done means the cause is identified, the import path works again, and the fix is verified.