Static variables for a message handler were used only in developer
build, while they were declared unconditionally.
That has lead to compiler warnings about unused variables in a
non developer build.
=> declare them only in developer build
=> move assignment and static method in front of the method,
that uses them.
Pick-to: 6.6 6.5
Change-Id: Ie06f91f7857130f08fd484a6e7319ddfd16c546b
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
366b4d3ae7