Video canvas mispositioned #556
Description
The video canvas sometimes ends up mispositioned after maximizing/unmaximizing the window:
I can reproduce it reliably by unmaximizing, resizing the window to make sure the video fits inside, and maximizing again.
(I tried bisecting because I don't remember encountering this in the past, but to my surprise all commits as far back as the 3.4.1 release had the bug. Maybe it depends on some dependency version?)