tdf#90255 FILESAVE:PPTX 'startAt' tag for bullet numbering is not exported

Problem Description :
XML Difference
Original :
<a:buAutoNum type="arabicPeriod" startAt="3"/>

Roundtrip :
<a:buAutoNum type="arabicPeriod"/>

Solution :
Added export support for 'startAt' tag of <a:buAutoNum> for pptx.

Change-Id: If86bce98e222795d851d4a5b3cbb65da5cee85fc
Reviewed-on: https://gerrit.libreoffice.org/15028Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>

oox/source/export/drawingml.cxx

@@ -1611,6 +1611,7 @@ void DrawingML::WriteParagraphNumbering( Reference< XPropertySet > rXPropSet, sa
     bool bHasFontDesc = false;
     OUString aGraphicURL;
     sal_Int16 nBulletRelSize = 0;
+    sal_Int16 nStartWith = 1;
 
     for ( sal_Int32 i = 0; i < nPropertyCount; i++ )
     {
@@ -1656,6 +1657,10 @@ void DrawingML::WriteParagraphNumbering( Reference< XPropertySet > rXPropSet, sa
             {
                 nBulletRelSize = *static_cast<sal_Int16 const *>(pValue);
             }
+            else if ( aPropName == "StartWith" )
+            {
+                nStartWith = *( (sal_Int16*)pValue );
+            }
             else if ( aPropName == "GraphicURL" )
             {
                 aGraphicURL = *static_cast<OUString const *>(pValue);
@@ -1704,6 +1709,7 @@ void DrawingML::WriteParagraphNumbering( Reference< XPropertySet > rXPropSet, sa
         {
             mpFS->singleElementNS(XML_a, XML_buAutoNum,
                                   XML_type, OUStringToOString(pAutoNumType, RTL_TEXTENCODING_UTF8).getStr(),
+                                  XML_startAt, nStartWith > 1 ? IS(nStartWith) : NULL,
                                   FSEND);
         }
         else

sd/qa/unit/export-tests.cxx

@@ -84,6 +84,7 @@ public:
     void testLinkedGraphicRT();
     void testImageWithSpecialID();
     void testTableCellFillProperties();
+    void testBulletStartNumber();
 #if !defined WNT
     void testBnc822341();
 #endif
@@ -107,6 +108,7 @@ public:
     CPPUNIT_TEST(testLinkedGraphicRT);
     CPPUNIT_TEST(testImageWithSpecialID);
     CPPUNIT_TEST(testTableCellFillProperties);
+    CPPUNIT_TEST(testBulletStartNumber);
 #if !defined WNT
     CPPUNIT_TEST(testBnc822341);
 #endif
@@ -781,6 +783,30 @@ void SdExportTest::testTableCellFillProperties()
     xDocShRef->DoClose();
 }
 
+void SdExportTest::testBulletStartNumber()
+{
+    ::sd::DrawDocShellRef xDocShRef = loadURL( getURLFromSrc("/sd/qa/unit/data/pptx/n90255.pptx"), PPTX );
+    xDocShRef = saveAndReload( xDocShRef, PPTX );
+
+    uno::Reference< drawing::XDrawPagesSupplier > xDoc(
+        xDocShRef->GetDoc()->getUnoModel(), uno::UNO_QUERY_THROW );
+
+    uno::Reference< drawing::XDrawPage > xPage(
+        xDoc->getDrawPages()->getByIndex(0), uno::UNO_QUERY_THROW );
+    SdDrawDocument *pDoc = xDocShRef->GetDoc();
+    CPPUNIT_ASSERT_MESSAGE( "no document", pDoc != NULL );
+
+    const SdrPage *pPage = pDoc->GetPage(1);
+    CPPUNIT_ASSERT_MESSAGE( "no page", pPage != NULL );
+    SdrTextObj *pTxtObj = dynamic_cast<SdrTextObj *>( pPage->GetObj(0) );
+    CPPUNIT_ASSERT_MESSAGE( "no text object", pTxtObj != NULL);
+    const EditTextObject& aEdit = pTxtObj->GetOutlinerParaObject()->GetTextObject();
+    const SvxNumBulletItem *pNumFmt = dynamic_cast<const SvxNumBulletItem *>(aEdit.GetParaAttribs(0).GetItem(EE_PARA_NUMBULLET));
+    CPPUNIT_ASSERT(pNumFmt);
+    CPPUNIT_ASSERT_EQUAL_MESSAGE( "Bullet's start number is wrong!", sal_Int16(pNumFmt->GetNumRule()->GetLevel(0).GetStart()), sal_Int16(3) );
+    xDocShRef->DoClose();
+}
+
 #if !defined WNT
 
 void SdExportTest::testBnc822341()