Opening, creating, closing or reverting a session in the middle of a
take dropped the recorder: the take was written to disk but never added
to any session. Quitting mid-take did the same, and on_exit didn't
finish the take either.
New, Open, Close, Revert and Quit now wait for the take: the engine
refuses them with "stop recording first", and their menu items are
greyed out while recording, as is Recover in the recovery window. Any
exit that still happens mid-take (closing the window, the system
quitting the app, a remote quit) finishes the take first and keeps the
session, take included, in the autosave folder for the next launch.
