Set layout direction of wxComboBox edit control only if it exists.

Doesn't update layout direction of edit control if wxComboBox is in read-only
mode because editor control doesn't exist in this case.

src/msw/combobox.cpp

@@ -716,6 +716,8 @@ void wxComboBox::SetLayoutDirection(wxLayoutDirection dir)
     // extended style flags), so its layout direction should be set using the
     // same extended flag as for ordinary window but reset simply with
     // alignment flags.
+    if ( !HasFlag(wxCB_READONLY) )
+    {
         if ( dir == wxLayout_RightToLeft )
         {
             wxUpdateLayoutDirection(GetEditHWND(), dir);
@@ -729,6 +731,7 @@ void wxComboBox::SetLayoutDirection(wxLayoutDirection dir)
                 ::SetWindowLongPtr(GetEditHWND(), GWL_STYLE, style);
             }
         }
+    }
 
     // Layout for the drop-down list also must be set explicitly.
     WinStruct<COMBOBOXINFO> info;