Invalidate best size of wxOSX wxChoice after its number of items changes.

This fixes the calculation of the initial best size as previously the default
value was not updated even if longer strings were added later.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72847 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/choice.h

@@ -93,6 +93,10 @@ protected:
     wxArrayString m_strings;
     wxChoiceDataArray m_datas ;
     wxMenu*    m_popUpMenu ;
+
+private:
+    // This should be called when the number of items in the control changes.
+    void DoAfterItemCountChange();
 };
 
 #endif