Fix wxGenericCollapsiblePane to expand frame's size.

wxGenericCollapsiblePane::DoGetBestSize() is dynamic, returning
different values for collapsed and open states. Therefore the control
must invalidate best sizes cache every time its state changes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72625 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/collpaneg.cpp

@@ -190,6 +190,8 @@ void wxGenericCollapsiblePane::Collapse(bool collapse)
     if ( IsCollapsed() == collapse )
         return;
 
+    InvalidateBestSize();
+
     // update our state
     m_pPane->Show(!collapse);