Do not let wxHeaderCtrl determine the minimum width

The minimum width will always be equal to the current size of the parent window (from wxGetClientRect).
As a result, controls using wxHeaderCtrl can never be shrunk (e.g. using SetSizeHints).
Problem is visible when a wxDataViewCtrl gets a lower DPI. The new minimum size is equal to the current size.

src/msw/headerctrl.cpp

@@ -195,7 +195,7 @@ wxSize wxHeaderCtrl::DoGetBestSize() const
         return wxControl::DoGetBestSize();
     }
 
-    return wxSize(wpos.cx, wpos.cy);
+    return wxSize(wxDefaultCoord, wpos.cy);
 }
 
 // ----------------------------------------------------------------------------