Fix High Dpi Support. Works now under Windows ande KDE/Plasma.

Commit 4a530820 was incomplete...

Qts scaling environment variables shall never be changed by application.
That way the user hasn't any chance to fix things himself. With setting
QT_AUTO_SCREEN_SCALE_FACTOR to 1 QtPass does not work under KDE/Plasma
and cannot even be fixed by setting Qts scaling environment variables.