It is possible to bring our player out of fullscreen mode without using
the provided views menu or keyboard shortcut, e.g. by pressing Escape.
Doing so leaves our state in the SUPERTHEATRE view, which omits
SUPERtheatre mode itself from the views menu. This commit fixes this by
switching our state to the THEATRE view.
Thanks to Aske Bisgaard Vammen for the report.