fix for assert when setting tooltip for a readonly combo (backported from the main branch)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_2_BRANCH@8531 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/tooltip.cpp

@@ -382,12 +382,13 @@ void wxToolTip::SetWindow(wxWindow *win)
     wxComboBox *combo = wxDynamicCast(control, wxComboBox);
     if ( combo )
     {
-        WXHWND hwndComboEdit = combo->GetEditHWND();
+        WXHWND hwndComboEdit = combo->GetWindowStyle() & wxCB_READONLY
+                                ? combo->GetHWND()
+                                : combo->GetEditHWND();
         if ( hwndComboEdit )
         {
             Add(hwndComboEdit);
         }
-        //else: it's ok for a combo to be read only, of course
     }
 }