coverity#1426167 refactor to be less obscure

no logic change intended

Change-Id: I10ef6038351b2808c2030aa55f05e078d80345ae
Reviewed-on: https://gerrit.libreoffice.org/46609Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/source/core/layout/atrfrm.cxx

@@ -2546,10 +2546,12 @@ bool SwFrameFormat::supportsFullDrawingLayerFillAttributeSet() const
 
 void SwFrameFormat::Modify( const SfxPoolItem* pOld, const SfxPoolItem* pNew )
 {
+    if (pNew)
+    {
         SwFormatHeader const *pH = nullptr;
         SwFormatFooter const *pF = nullptr;
 
-    const sal_uInt16 nWhich = pNew ? pNew->Which() : 0;
+        const sal_uInt16 nWhich = pNew->Which();
 
         if( RES_ATTRSET_CHG == nWhich )
         {
@@ -2599,6 +2601,7 @@ void SwFrameFormat::Modify( const SfxPoolItem* pOld, const SfxPoolItem* pNew )
             SwFrameFormat *pFormat = GetDoc()->getIDocumentLayoutAccess().MakeLayoutFormat( RndStdIds::FOOTER, nullptr );
             const_cast<SwFormatFooter *>(pF)->RegisterToFormat( *pFormat );
         }
+    }
 
     SwFormat::Modify( pOld, pNew );