Handle any queued messages before attempting to dispatch
any newly received messages. This ensures that messages are
processed in the order they were sent.
Add a regression test for this bug using code adapted
from the bug report by Pascal Weisser. Because of the
nature of the bug, this new test does not always fail
even when compiled with affected versions of Qt though.
Fixes: QTBUG-105457
Pick-to: 6.2 6.5
Change-Id: I2725f3450ad537d63d6660e21645ac2c578e1768
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
859ef05633