coverity#1426168 Dereference after null check

Change-Id: Ib3ae45a7b012775ee7d540a565c0324f8dcf456e
Reviewed-on: https://gerrit.libreoffice.org/46611Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/source/core/layout/fly.cxx

@@ -758,7 +758,7 @@ void SwFlyFrame::UpdateAttr_( const SfxPoolItem *pOld, const SfxPoolItem *pNew,
             if ( FrameSizeChg( rNew ) )
                 NotifyDrawObj();
             rInvFlags |= 0x7F;
-            if ( RES_FMT_CHG == nWhich )
+            if (pOld && RES_FMT_CHG == nWhich)
             {
                 SwRect aNew( GetObjRectWithSpaces() );
                 SwRect aOld( getFrameArea() );