Fix importing in source build with no qt version

Before we would only offer widgets for targets which had at least
a qt version. Thus it was impossible to import a in source desktop
build if the user had no qt version for the desktop in the settings.

Change-Id: Ib8e04b1569ac3499c11c5cfda6c708f5fd408144
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>