Fix and improve the test cases.

setupapi: SetupDiGetDeviceRegistryProperty should return ERROR_INVALID_DATA when buffer size is not 0 but buffer is NULL.

setupapi: SetupDiGetDeviceRegistryProperty should return ERROR_INSUFFICIENT_BUFFER when buffer size is insufficient.

Use consistent naming for all event handlers.

server: Make enum_desktop enumerate all the desktops on the window station with the DESKTOP_ENUMERATE right.