do not iterate over all bookmarks in SwTxtNode::Update()

3f987218 introduced new API for fast finding of marks to a specific text node,
so use that (code itself based on cb46aaf2).
This makes mailmerge faster (since it can create a huge document, and especially
with the change to use UNO bookmarks to mark starts of MM documents inside
the larger single document there can be a large number of marks).

Change-Id: I30ec69acf423e9a62fae5f5492ed8744cb727a56

sw/source/core/txtnode/ndtxt.cxx

@@ -1067,12 +1067,19 @@ void SwTxtNode::Update(
         {
             bool bAtLeastOneBookmarkMoved = false;
             bool bAtLeastOneExpandedBookmarkAtInsertionPosition = false;
-            const IDocumentMarkAccess* const pMarkAccess = getIDocumentMarkAccess();
-            for ( IDocumentMarkAccess::const_iterator_t ppMark = pMarkAccess->getAllMarksBegin();
-                ppMark != pMarkAccess->getAllMarksEnd();
-                ++ppMark )
-            {
-                const ::sw::mark::IMark* const pMark = ppMark->get();
+            // A text node already knows its marks via its SwIndexes.
+            std::set<const sw::mark::IMark*> aSeenMarks;
+            const SwIndex* next;
+            for (const SwIndex* pIndex = GetFirstIndex(); pIndex; pIndex = next )
+            {
+                next = pIndex->GetNext();
+                const sw::mark::IMark* pMark = pIndex->GetMark();
+                if (!pMark)
+                    continue;
+                // Only handle bookmarks once, if they start and end at this node as well.
+                if (aSeenMarks.find(pMark) != aSeenMarks.end())
+                    continue;
+                aSeenMarks.insert(pMark);
                 const SwPosition* pEnd = &pMark->GetMarkEnd();
                 SwIndex & rEndIdx = const_cast<SwIndex&>(pEnd->nContent);
                 if( this == &pEnd->nNode.GetNode() &&