One could guess it by assuming that disconnecting for a destroyed
receiver and disconnect() with given receiver use the same
implementation, but without closely knowing the implementation a
reader of the documentation can't know for sure.
Also add a test to prove that what the new documentation says is
really true.
Also remove an unnecessary negation in the preceding sentence.
Change-Id: I9d24442bb1a4646b89f969bad1a4d0e1eafa7534
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
7406949858