Frozen forms cause javascript error: currentform is null

• this is due to fact that no form tag is present for frozen forms, but code in /lib/yui/formchangechecker/formchangechecker.js::init() assumes form present.
  Suggested code fix:

  --- a/lib/yui/formchangechecker/formchangechecker.js

  +++ b/lib/yui/formchangechecker/formchangechecker.js

  @@ -23,6 +23,11 @@ YUI.add('moodle-core-formchangechecker',

  // Add change events to the form elements

  var currentform = Y.one(formid);

  + if (!currentform) {

  + return;

  + }

  currentform.delegate('change', M.core_formchangechecker.set_form_changed, 'input', this);

  currentform.delegate('change', M.core_formchangechecker.set_form_changed, 'textarea', this);

  currentform.delegate('change', M.core_formchangechecker.set_form_changed, 'select', this);