tdf#70346 MM: don't restore section visibility

Mail merging the current document is expected to change the
source document. So there is no need to try to restore the pre-MM
document, even the visibility. In the end any effort is futile,
as field changes cannot be undone.

Even worse: it introduced a regression using the "data to fields"
function from the data source manager (F4), which would never
set the correct section visibility.

We need to copy the document to prevent changes to the source
document and skip the quite probably unexpected save in MM.

Change-Id: I814905f1566a63b2ee14cb5f6d08da34c05942aa

sw/source/uibase/dbui/dbmgr.cxx

@@ -453,11 +453,6 @@ bool SwDBManager::MergeNew( const SwMergeDescriptor& rMergeDesc )
 
     DELETEZ( pImpl->pMergeData );
 
-    // Recalculate original section visibility states, as field changes aren't
-    // tracked (not undo-able).  Has to be done, after pImpl->pMergeData is
-    //  gone, otherwise merge data is used for calculation!
-    rMergeDesc.rSh.SwViewShell::UpdateFlds();
-
     bInMerge = false;
 
     return bRet;