Invalidate wxListBox best size immediately without waiting for idle time.

Since r53743 the listbox best size was only invalidated during idle time but
this meant that it could be laid out using incorrect old best size. So while
we still defer (expensive) horizontal extent calculation until later, do
invalidate the best size immediately to ensure the listbox is laid out
correctly.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64246 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/listbox.h

@@ -145,6 +145,8 @@ public:
     // returns true if the platform should explicitly apply a theme border
     virtual bool CanApplyThemeBorder() const { return false; }
 
+    virtual void OnInternalIdle();
+
 protected:
     virtual wxSize DoGetBestClientSize() const;
 
@@ -164,8 +166,8 @@ protected:
     // this can't be called DoHitTest() because wxWindow already has this method
     virtual int DoHitTestList(const wxPoint& point) const;
 
-    bool m_updateHorizontalExtent;
-    virtual void OnInternalIdle();
+    // free memory (common part of Clear() and dtor)
+    void Free();
 
     unsigned int m_noItems;
 
@@ -175,6 +177,14 @@ protected:
 #endif
 
 private:
+    // call this when items are added to or deleted from the listbox or an
+    // items text changes
+    void MSWOnItemsChanged();
+
+    // flag indicating whether the max horizontal extent should be updated,
+    // i.e. if we need to call SetHorizontalExtent() from OnInternalIdle()
+    bool m_updateHorizontalExtent;
+
     DECLARE_DYNAMIC_CLASS_NO_COPY(wxListBox)
 };