Don't emit documentClosed repeatedly for the same document
Numerous slots are connected to this signal. They are all invoked repeatedly and redundantly. The number of the invocations equals one plus the number of times the closed document was activated via reopening (e.g. by Most-Recently-Used Document Switcher or by Document View).
Connecting DocumentController::notifyDocumentClosed
with
Qt::UniqueConnection
connection type in openDocumentInternal()
ensures
that the documentClosed
signal is emitted once.