tdf#120801: The background colour is active when inserting a header

In this patch, the active background colour is disabled by passing null value as default to the FillStyleItem.

Previous Result: Background colour was still active even after inserting a header.

Result after applying this patch: Background is now remain disabled/inactive.

Change-Id: I5e8d22af338ef8ec93aa0e93d338ab8129fdc893
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/113468
Tested-by: Justin Luth <justin_luth@sil.org>
Reviewed-by: Justin Luth <justin_luth@sil.org>
diff --git a/sw/source/uibase/wrtsh/wrtsh1.cxx b/sw/source/uibase/wrtsh/wrtsh1.cxx
index bb14ad2..b26af83 100644
--- a/sw/source/uibase/wrtsh/wrtsh1.cxx
+++ b/sw/source/uibase/wrtsh/wrtsh1.cxx
@@ -28,6 +28,7 @@

#include <hintids.hxx>
#include <sot/exchange.hxx>
#include <svx/xfillit0.hxx>
#include <svx/hdft.hxx>
#include <svx/svdview.hxx>
#include <svl/itemiter.hxx>
@@ -1895,6 +1896,8 @@ void SwWrtShell::ChangeHeaderOrFooter(
                        const_cast<SwFrameFormat*>(rMaster.GetHeader().GetHeaderFormat()) :
                        const_cast<SwFrameFormat*>(rMaster.GetFooter().GetFooterFormat());
                    pFormat->SetFormatAttr( aUL );
                    XFillStyleItem aFill(drawing::FillStyle_NONE);
                    pFormat->SetFormatAttr(aFill);
                }
            }
            if( bChgd )