WinRT: Check whether default sensors were obtained successfully

In case of an unsuccessful call of the GetDefault function the returned
HRESULT does not have the FAILED status but the returned sensor is 0.

Task-number: QTBUG-39698
Change-Id: I42a8327c1d7687ab7a8ca71be5a2234b2c4e0b38
Reviewed-by: Andrew Knight <andrew.knight@digia.com>