Applied patch in #12279: in wxRichTextCtrl, when wxRE_READONLY is set, the undo, redo function should be disabled

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@67023 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/richtext/richtextctrl.cpp

@@ -2718,12 +2718,12 @@ void wxRichTextCtrl::Redo()
 
 bool wxRichTextCtrl::CanUndo() const
 {
-    return GetCommandProcessor()->CanUndo();
+    return GetCommandProcessor()->CanUndo() && IsEditable();
 }
 
 bool wxRichTextCtrl::CanRedo() const
 {
-    return GetCommandProcessor()->CanRedo();
+    return GetCommandProcessor()->CanRedo() && IsEditable();
 }
 
 // ----------------------------------------------------------------------------