Fixes a case where a video page could still offer a generic "Stream" download
instead of the quality list. The previous release hid those links only while
the quality list loaded successfully, so they reappeared whenever the desktop
app was restarting or not running. They are now withheld in all cases. The
toolbar badge also no longer counts links that are never offered.

Fixed: on some video pages the menu could offer a generic "Stream" download
instead of the list of qualities. That link points at one internal piece of
the video rather than the video itself, so it produced a broken or silent
file. Those links are no longer offered.

Improved: the popup now loads the available qualities as soon as you open it,
instead of waiting for you to press a button.

Improved: when the Downloader Pro desktop app isn't running, the popup now
says so clearly, instead of quietly falling back to showing raw stream links.