Avoid a hang if we're dragging a tab to a notebook that's a child of the original tab

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@47662 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/aui/auibook.cpp

@@ -3426,6 +3426,17 @@ void wxAuiNotebook::OnTabEndDrag(wxCommandEvent& command_evt)
                 int src_idx = evt.GetSelection();
                 wxWindow* src_page = src_tabs->GetWindowFromIdx(src_idx);
 
+                // Check that it's not an impossible parent relationship
+                wxWindow* p = nb;
+                while (p && !p->IsTopLevel())
+                {
+                    if (p == src_page)
+                    {
+                        return;
+                    }
+                    p = p->GetParent();
+                }
+
                 // get main index of the page
                 int main_idx = m_tabs.GetIdxFromWindow(src_page);