Like in all other places. This way the resulting QMenu is correctly
parented so it will show up at the proper position even on platforms
which do not have a way to position top-level windows.
Task-number: QTBUG-29025
Change-Id: I2aa6fe73699379029c44a3f379366a2133753190
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>