QFileDialog: save and restore all settings even if widgets not used

Some applications may use native file dialogs and some may use the
widget implementation, but QFileDialog always saves all settings to
the same place each time it destroyed.  So it is important to remember
all settings read in restoreState and put them back in saveState.
This bug was introduced by 37ca2224eca671200a2710f57f970d2993e62aa5

Task-number: QTBUG-36888
Change-Id: Ied1db83817480312e963a042784d7bdd16f0a2b1
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>