Spreadsheet: fix owner property reference in PropertySheet

PropertySheet used to only work when refereceing its own cell either
through cell address or alias. It does not work for reference to other
property of the owner Spreadsheet object.

src/Mod/Spreadsheet/App/Sheet.cpp

@@ -1568,7 +1568,8 @@ void Sheet::onChanged(const App::Property *prop) {
         for(auto &range : tmp)
             rangeUpdated(range);
     }
-    
+    else
+        cells.slotChangedObject(*this, *prop);
     App::DocumentObject::onChanged(prop);
 }