Set the initial size of the expanded ribbon panel correctly.

We need to set the client size of the frame showing the panel to the panel
size and not the full frame size.

Closes #13850.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70456 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/ribbon/panel.cpp

@@ -775,6 +775,7 @@ bool wxRibbonPanel::ShowExpanded()
 
     m_expanded_panel->Realize();
     Refresh();
+    container->SetMinClientSize(size);
     container->Show();
     m_expanded_panel->SetFocus();