D6249: FindQHelpGenerator: avoid picking up Qt4 version

[Michael Palimaka]

palimaka added a reviewer: kossebau.

REPOSITORY
  R240 Extra CMake Modules

REVISION DETAIL
  https://phabricator.kde.org/D6249

To: palimaka, #frameworks, kossebau
Cc: asturmlechner, #build_system