tests: always use expected_type from mock dbus
tests: always use expected_type from mock dbus

Always call dconf_engine_call_handle_get_expected_type() from the mock
dbus backend, even if the handle is NULL.  This matches the behaviour of
the real D-Bus backends and would have caught the bug fixed in the last
commit.

GNOME/dconf,GNOME/dconf,GNOME/dconf,GNOME/dconf