move it to when the dialog is closed rather than trying to
launch it as soon as any modifications take place because
those are happening during threaded code and the restart
is always cancelled by the dialog itself leading to repeated
restart dialogs

Now at least it doesn't crash, but if we open an oxt on the command
line, a restart will reopen it, which is probably not what we want.
Maybe this restart on an extension modification is a bad idea in
the first place.

Change-Id: Ib7d6179e6703ed3353fce44c3e54f5be1c1dfa68