Fix data race in QCoreApplicationPrivate::sendThroughApplicationEventFilters()

The assertion has the acquire fence at the wrong place:

- QThreadData::thread isn't dereferenced, so the acquire fence on its
  load() isn't needed.

- QObjectPrivate::threadData, however, _is_ dereferenced, so an
  acquire fence is needed; the relaxed load() is insufficient.

Swapping the loadAcquire() and the loadRelaxed() fixes both issues.

Pick-to: 6.4 6.3 6.2 5.15
Change-Id: Iee964490e93ebc323c188e616bf0d448f91fb2b5
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/corelib/kernel/qcoreapplication.cpp

@@ -1132,7 +1132,7 @@ static bool doNotify(QObject *receiver, QEvent *event)
 bool QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject *receiver, QEvent *event)
 {
     // We can't access the application event filters outside of the main thread (race conditions)
-    Q_ASSERT(receiver->d_func()->threadData.loadRelaxed()->thread.loadAcquire() == mainThread());
+    Q_ASSERT(receiver->d_func()->threadData.loadAcquire()->thread.loadRelaxed() == mainThread());
 
     if (extraData) {
         // application event filters are only called for objects in the GUI thread