sw_redlinehide: reinit m_pMergedPara on split node

Change-Id: I560f1cdb537fa848fdbaf719424d4e6608ceda0d

sw/source/core/layout/ssfrm.cxx

@@ -437,6 +437,7 @@ SwContentFrame::~SwContentFrame()
 void SwTextFrame::RegisterToNode(SwTextNode & rNode)
 {
     assert(&rNode != GetRegisteredIn());
+    m_pMergedPara = sw::CheckParaRedlineMerge(*this, rNode);
     rNode.Add( this );
 }