Update the field widths on demand in wxStatusBarGeneric.

This ensures that the value returned from GetFieldRect() is always up to date,
even when this method is called from the user-defined wxEVT_SIZE handler, i.e.
before our own OnSize() could run.

Also remove the now unneeded hack with calling the base class OnSize() from
the statbar sample.

Closes #14268.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71365 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/statusbr.h

@@ -91,8 +91,9 @@ protected:
     // common part of all ctors
     void Init();
 
-    // the last known height of the client rect
-    int               m_lastClientHeight;
+    // the last known size, fields widths must be updated whenever it's out of
+    // date
+    wxSize m_lastClientSize;
 
     // the absolute widths of the status bar panes in pixels
     wxArrayInt        m_widthsAbs;
@@ -106,6 +107,9 @@ protected:
     virtual wxSize DoGetBestSize() const;
 
 private:
+    // Update m_lastClientSize and m_widthsAbs from the current size.
+    void DoUpdateFieldWidths();
+
     DECLARE_EVENT_TABLE()
     DECLARE_DYNAMIC_CLASS_NO_COPY(wxStatusBarGeneric)
 };