We can only start timers in threads started via QThread, and even then
we cannot assume that the thread runs an event loop. So only start the
timer when we are in the main thread.
Add a test that verifies that we don't get the warning message.
Pick-to: 6.2
Change-Id: I40d7d9ff115720f9ecd3eedaebbade2643daf843
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
132d6d0127