Disable error message box on WinRT

While exception handling methods are not available on WinRT, the debug
mode ones are. This way we can suppress error dialogs from popping up
like on desktop windows.

Change-Id: Id6e9666af9274d373e7d46e3f9e44892a2bd0dbc
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>