QtVersion: Fix incorrect check for installation

Task-number: QTCREATORBUG-7847
Change-Id: I0af0c02b2ab04a82def5d0e9a1baee0d95919a16
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>
Reviewed-by: Loïc Yhuel <loic.yhuel@softathome.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>