If the QFuture is canceled because the associated QPromise has been
destroyed, we still need to run its continuations (i.e. onCanceled
handler, if it's attached), so replaced the cleanContinuation() call
inside ~QPromise() with runContinuation(), which will also take care of
cleaning the continuation.
[ChangeLog][QtCore][Important Behavior Changes] QFuture now runs its
continuations when its associated QPromise has been destroyed.
Previously, if a QFuture was canceled because the associated QPromise
has been destroyed, its continuations were skipped.
Fixes: QTBUG-103992
Pick-to: 6.4 6.3 6.2
Change-Id: Ie05bc760c96c349aade8adb8d2fe5263aff8efac
Reviewed-by: Marc Mutz <marc.mutz@qt.io>