When Qt is not driving the event dispatching, the event loop level
of the thread will stay 0. As a result, we will not automatically
bump the deferred delete event's scope level to 1 when the deferred
delete happens from a code path that doesn't raise the scope level
via QScopedScopeLevelCounter, leaving the event with loop and scope
level 0.
As we only process these 0+0 deferred delete events automatically from
QCoreApplicationPrivate::execCleanup(), which is not going to be called
when the app doesn't call QCoreAppliction::exec(), we were failing to
process the deferred deletes both during the application's runtime,
as well as on shutdown.
Task-number: QTBUG-120124
Fixes: QTBUG-117975
Pick-to: 6.7 6.6 6.5
Change-Id: I2b8accb432517a48370923ee2d760f8e2e4a8055
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
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