Currently there is no need to hook DefDlgProc(). Tests show that dialog theming shouldn't be
implemented in DefDlgProc().

Also fix a double free bug because WM_DESTROY in UXTHEME_DefDlgProc() calls CloseThemeData() even
when the theme handle is not opened when handling WM_CREATE in UXTHEME_DefDlgProc(). The bug can
be demonstrated by running comctl32/tests/propsheet.c tests with Light theme.
Signed-off-by: Zhiyi Zhang <zzhang@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>