Fix QSystemBatteryInfo crash on Windows.
Fix QSystemBatteryInfo crash on Windows.

QSystemBatteryInfo crashed when the power adapter was plugged or
unplugged.

Task-number: QTMOBILITY-2008

tmcguire/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility