Fix Dom_html.Keyboard_code.of_event

For the standard location (0) we were ignoring the `code` property of
the keyboard event and using the deprecated `keyCode` property instead.

Author: vouillon

lib/js_of_ocaml/dom_html.ml

@@ -3383,7 +3383,7 @@ module Keyboard_code = struct
     | 1 -> run_next (get_key_code evt) try_key_code_left
     | 2 -> run_next (get_key_code evt) try_key_code_right
     | 3 -> run_next (get_key_code evt) try_key_code_numpad
-    | _ -> make_unidentified
+    | _ -> fun v -> v
 
   let ( |> ) x f = f x