Else some hash key/value pairs are not initialized at all.
This causes for example:
"Use of uninitialized value" warnings in FIJITestsViewer.pm line 1137

With this change we also set the defaults unconditionally when loaded
by the GUI. This also requires $global_settings_ref to be passed to
_set_defaults() which was using an inexistent $self->{'settings'} so far.