also assert in generic GetSelection() if the control is in multiselection mode, for consistency with wxMSW and other controls

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@49571 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/treectlg.h

@@ -112,7 +112,13 @@ public:
     // ----------
 
     virtual wxTreeItemId GetRootItem() const { return m_anchor; }
-    virtual wxTreeItemId GetSelection() const { return m_current; }
+    virtual wxTreeItemId GetSelection() const
+    {
+        wxASSERT_MSG( !HasFlag(wxTR_MULTIPLE),
+                       wxT("must use GetSelections() with this control") );
+
+        return m_current;
+    }
     virtual size_t GetSelections(wxArrayTreeItemIds&) const;
 
     virtual wxTreeItemId GetItemParent(const wxTreeItemId& item) const;