Blank space on top when window width is resized to less than some threshold

[rotemdan]

When window width is resized to be smaller than some size (~800-1200 pixels) YouTube switches to a different player layout, where #player-theater-container exists but is empty and instead it puts the player in a different container #columns. This causes a large blank space at the top of the page.

Simple solution: disable the script when #player-theater-container is empty. Implementing this is not trivial though, and as this behavior might be changed in the future so I'm leaving this open for now.