fdo#74981: cutting nothing should do nothing, should fix field dupes

Change-Id: I8a8c9bfcd0943904384bb12b510a050ef8df9adf
diff --git a/sw/source/core/txtnode/ndtxt.cxx b/sw/source/core/txtnode/ndtxt.cxx
index e212d55..017c4b6 100644
--- a/sw/source/core/txtnode/ndtxt.cxx
+++ b/sw/source/core/txtnode/ndtxt.cxx
@@ -1930,6 +1930,8 @@ OUString SwTxtNode::InsertText( const OUString & rStr, const SwIndex & rIdx,
void SwTxtNode::CutText( SwTxtNode * const pDest,
            const SwIndex & rStart, const sal_Int32 nLen )
{
    if(nLen == 0)
        return;
    if(pDest)
    {
        SwIndex aDestStt(pDest, pDest->GetTxt().getLength());