Make the wxDataViewItem(void*) constructor explicit.

Not having this as an implicit one made it possible to create
wxDataViewItem from any pointer without realizing it, leading to hard to
debug crashes later.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68621 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/dataview.h

@@ -81,10 +81,11 @@ extern WXDLLIMPEXP_DATA_ADV(const char) wxDataViewCtrlNameStr[];
 class WXDLLIMPEXP_ADV wxDataViewItem
 {
 public:
-    wxDataViewItem( void* id = NULL )
-        { m_id = id; }
-    wxDataViewItem( const wxDataViewItem &item )
-        { m_id = item.m_id; }
+    wxDataViewItem() : m_id(NULL) {}
+    wxDataViewItem(const wxDataViewItem &item) : m_id(item.m_id) {}
+
+    wxEXPLICIT wxDataViewItem(void* id) : m_id(id) {}
+
     bool IsOk() const                  { return m_id != NULL; }
     void* GetID() const                { return m_id; }
     operator const void* () const      { return m_id; }