Download choice modal loses focus when non-text response is received from CLI URL

[makew0rld]

Run amfora gemini.thebackupbox.net/radio. The URL is to a page that returns audio/mpeg. The page is loading, then the download choice modal pops up, then the new tab page loads behind it and takes focus, meaning the user can't select a download choice.

[makew0rld]

Related to #281, if the modal was blocking this wouldn't happen

[mntn-xyz]

This also happens if the URL triggers an external handler, for instance amfora https://example.com causes the Info dialog to be stuck on screen after the configured browser is opened.

[makew0rld]

Closed by #284, thanks @awfulcooking!