Clarify documentation for wxPropertyGridEvent::GetProperty()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63711 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/propgrid/propgrid.h

@@ -1130,6 +1130,11 @@ public:
 
     /**
         Returns property associated with this event.
+
+        @remarks You should assume that this property can always be NULL.
+                 For instance, wxEVT_PG_SELECTED is emitted not only when
+                 a new property is selected, but also when selection is
+                 cleared by user activity.
     */
     wxPGProperty* GetProperty() const;