The HDMI display on the Playbook is listed, but (normally) unattached,
and hence generates an error if we attempt to register for events. This
patch avoids the warning; a future change will actually watch for screens
being attached / detached and update the QPlatformScreens and event
registration correctly.
Change-Id: I5a9cc773648d50f657fe1b3611fd42495ca7e836
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>