fix LD_LIBRARY_PATH manipulation in uic calls not being make-escaped

the evaluator has the bug that function arguments are inherited.
work around that by passing an explicitly empty 3rd parameter to
qtAddTargetEnv().
proper fix upcoming in less critical branch.

Change-Id: Ic45cc890abaa6271985590d4ebe02c96bff6dec4
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>