fdo#78420 File is getting corrupted after exported from LO.

It is not creating .rels file for Header3.xml. While the Header3.xml contains the images.

Change-Id: I3d1eb187eaf23fc05783fbfd3576d9a585de791f
Reviewed-on: https://gerrit.libreoffice.org/9286Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>

sw/qa/extras/ooxmlexport/ooxmlexport.cxx

@@ -3283,6 +3283,21 @@ DECLARE_OOXMLEXPORT_TEST(testContentTypeOLE, "fdo77759.docx")
                 "/word/embeddings/oleObject1.xlsx");
 }
 
+DECLARE_OOXMLEXPORT_TEST(testfdo78420, "fdo78420.docx")
+{
+    xmlDocPtr pXmlHeader = parseExport("word/header3.xml");
+
+    if (!pXmlHeader)
+       return;
+
+    xmlDocPtr pXmlHeaderRels = parseExport("word/_rels/header3.xml.rels");
+    if(!pXmlHeaderRels)
+       return;
+
+    assertXPath(pXmlHeaderRels,"/rels:Relationships/rels:Relationship[1]","Id","rId1");
+}
+
+
 DECLARE_OOXMLEXPORT_TEST(testPageBreakInFirstPara,"fdo77727.docx")
 {
     /* Break to next page was not exported if it is in first paragraph of the section.

sw/source/filter/ww8/docxattributeoutput.cxx

@@ -3567,6 +3567,11 @@ void DocxAttributeOutput::WriteSrcRect(const SdrObject* pSdrObj )
     }
 }
 
+void DocxAttributeOutput::ClearGraphicCache()
+{
+    m_aRelIdCache.clear();
+}
+
 void DocxAttributeOutput::FlyFrameGraphic( const SwGrfNode* pGrfNode, const Size& rSize, const SwFlyFrmFmt* pOLEFrmFmt, SwOLENode* pOLENode, const SdrObject* pSdrObj )
 {
     OSL_TRACE( "TODO DocxAttributeOutput::FlyFrameGraphic( const SwGrfNode* pGrfNode, const Size& rSize, const SwFlyFrmFmt* pOLEFrmFmt, SwOLENode* pOLENode, const SdrObject* pSdrObj  ) - some stuff still missing" );

sw/source/filter/ww8/docxattributeoutput.hxx

@@ -358,6 +358,7 @@ public:
 
     void WriteBookmarks_Impl( std::vector< OUString >& rStarts, std::vector< OUString >& rEnds );
     void WriteAnnotationMarks_Impl( std::vector< OUString >& rStarts, std::vector< OUString >& rEnds );
+    void ClearGraphicCache();
 
 private:
     /// Initialize the structures where we are going to collect some of the paragraph properties.

sw/source/filter/ww8/docxexport.cxx

@@ -711,6 +711,10 @@ void DocxExport::WriteHeaderFooter( const SwFmt& rFmt, bool bHeader, const char*
     // do the work
     WriteHeaderFooterText( rFmt, bHeader );
 
+    //When the stream changes the cache which is maintained for the graphics in case of alternate content is not cleared.
+    //So clearing the alternate content graphic cache.
+    m_pAttrOutput->ClearGraphicCache();
+
     // switch the serializer back
     m_pAttrOutput->SetSerializer( m_pDocumentFS );
     m_pVMLExport->SetFS( m_pDocumentFS );