don't assert when ExpandAll() is called on hidden root item (fixes 1765566, replaces patch 1768282)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48097 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/treebase.cpp

@@ -193,7 +193,9 @@ void wxTreeCtrlBase::ExpandAllChildren(const wxTreeItemId& item)
 {
     // expand this item first, this might result in its children being added on
     // the fly
-    Expand(item);
+    if ( item != GetRootItem() || !HasFlag(wxTR_HIDE_ROOT) )
+        Expand(item);
+    //else: expanding hidden root item is unsupported and unnecessary
 
     // then (recursively) expand all the children
     wxTreeItemIdValue cookie;