Fix harmless gcc initialization order warning.

Put the initializes in wxDataViewTreeNode constructor initialization list in
order of their declaration.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69282 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/datavgen.cpp

@@ -322,8 +322,8 @@ class wxDataViewTreeNode
 {
 public:
     wxDataViewTreeNode(wxDataViewTreeNode *parent, const wxDataViewItem& item)
-        : m_item(item),
+        : m_parent(parent),
-          m_parent(parent),
+          m_item(item),
           m_branchData(NULL)
     {
     }