fdo#70861: cui: fix crash in SvxExtParagraphTabPage

SvxExtParagraphTabPage::Reset() must not request a pool default for
SID_ATTR_PARA_PAGENUM because it simply does not exist; the item is
backed by a member of SwPageDesc in Writer.

Change-Id: I9b157f048cd986566f9b01f3677b53d5974b6c8d

cui/source/tabpages/paragrph.cxx

@@ -1552,7 +1552,7 @@ void SvxExtParagraphTabPage::Reset( const SfxItemSet* rSet )
 
     _nWhich = GetWhich( SID_ATTR_PARA_PAGENUM );
 
-    if ( rSet->GetItemState(_nWhich) >= SfxItemState::DEFAULT )
+    if (rSet->GetItemState(_nWhich) >= SfxItemState::SET)
     {
         const sal_uInt16 nPageNum =
             static_cast<const SfxUInt16Item&>(rSet->Get( _nWhich ) ).GetValue();