Hide combobox popup when it is hidden itself in wxMSW.

It was possible to hide the main part of a combobox control but keep its popup
shown and this notably happened in wxGrid when TAB was pressed while a
wxChoice cell editor was dropped down.

Avoid this Cheshire combobox syndrome by explicitly dismissing the popup when
a combobox is hidden.

Closes #3113.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71104 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/choice.h

@@ -66,6 +66,8 @@ public:
                 const wxValidator& validator = wxDefaultValidator,
                 const wxString& name = wxChoiceNameStr);
 
+    virtual bool Show(bool show = true);
+
     virtual void SetLabel(const wxString& label);
 
     virtual unsigned int GetCount() const;