Update generated_code.md again

This brings in the one change from commit c6a85f2.

Signed-off-by: Uli Schlachter <psychon@znc.in>

doc/generated_code.md

@@ -1038,7 +1038,7 @@ impl CreateWindowAux {
         result
     }
     fn serialize_into(&self, bytes: &mut Vec<u8>, value_mask: u32) {
-        let _ = value_mask;
+        assert_eq!(self.switch_expr(), u32::from(value_mask), "switch `value_list` has an inconsistent discriminant");
         if let Some(background_pixmap) = self.background_pixmap {
             background_pixmap.serialize_into(bytes);
         }