coverity#1288894 Dereference after null check, golden

regression from

commit 553a058e
Date:   Sat Mar 14 20:43:43 2015 +0100

    core: dont use 'shortcut' that is longer than the original

    Change-Id: I0154e484a4f4d6ce6672ddf35d1869157a61f71e

Change-Id: I4159a5caf492900bcfb863bc0bc5cf59a47a311c

sw/source/core/txtnode/ndtxt.cxx

@@ -312,7 +312,8 @@ static void lcl_ChangeFtnRef( SwTxtNode &rNode )
             {
                 if( !pFrm )
                 {
-                    if(!SwIterator<SwCntntFrm,SwTxtNode>( rNode ).First())
+                    pFrm = SwIterator<SwCntntFrm,SwTxtNode>(rNode).First();
+                    if (!pFrm)
                         return;
                 }
                 SwTxtFtn *pAttr = static_cast<SwTxtFtn*>(pHt);