tdf#147802 don't trigger fade timer already shown/hidden

once they widgets are created and hidden, they are getting triggered to
update contents on pretty much all layout/draw events even though they
are already in the visibility state they are asked to enter.

Change-Id: I6078a5f322c88f0380ac42537b4921af1c56add5
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/142708
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/sw/source/uibase/docvw/HeaderFooterWin.cxx b/sw/source/uibase/docvw/HeaderFooterWin.cxx
index ce703c6..81f9121 100644
--- a/sw/source/uibase/docvw/HeaderFooterWin.cxx
+++ b/sw/source/uibase/docvw/HeaderFooterWin.cxx
@@ -274,6 +274,9 @@ void SwHeaderFooterWin::ShowAll(bool bShow)
    m_xMenuButton->set_visible(!bIsEmptyHeaderFooter);
    m_xPushButton->set_visible(bIsEmptyHeaderFooter);

    if (m_bIsAppearing == bShow)
        return;

    m_bIsAppearing = bShow;

    if (m_aFadeTimer.IsActive())