Ensures that QStyleOption is correctly initialized.
This prevents possible styling issues due to
QStyleOption's reporting version 0, see qstyleoption_cast.
This enables users to handle more cases in their QProxyStyle.
For now the test is only used for QCommonStyle.
Change-Id: I768db00b12b46890343fffe44e4f562762e9cf80
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>