tdf#114836, only set changed SfxItemSet properties

By always setting all existing properties again the calls started
to differ between XMultiPropertySet::setPropertyValues and
XPropertySet::setPropertyValue. This patch reduces the changes in
the called methods. We can not avoid slight differences but at least
the risk is minimized that something is unexpectedly changed.

Change-Id: I5866db7be2829e6aba930f620f45db655df4e3f7
Reviewed-on: https://gerrit.libreoffice.org/63854
Tested-by: Jenkins
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

svx/source/unodraw/unoshape.cxx

@@ -1617,7 +1617,11 @@ void SvxShape::_setPropertyValue( const OUString& rPropertyName, const uno::Any&
     {
         if( mpImpl->mpItemSet == nullptr )
         {
-            mpImpl->mpItemSet = GetSdrObject()->GetMergedItemSet().Clone();
+            mpImpl->mpItemSet.reset(new SfxItemSet( GetSdrObject()->getSdrModelFromSdrObject().GetItemPool(),  {{pMap->nWID, pMap->nWID}}));
+        }
+        else
+        {
+            mpImpl->mpItemSet->MergeRange(pMap->nWID, pMap->nWID);
         }
         pSet = mpImpl->mpItemSet.get();
     }