Webform doesn't honor/check form_state['redirect'] for programmatic overrides

Problem/Motivation

If a user sets the $form_state['redirect'] via custom submit handler, webform module will not use it. Instead, it will always check and implement the redirects in the settings. Here is the line in which it does this check in the webform_client_form_submit(), https://git.drupalcode.org/project/webform/blob/08ff0884ac3d4f98324ddadf....

Steps to replicate

* Create form
* create hook_form_alter() updating redirect value

function hook_form_alter(&$form, &$form_state, $form_id) {
  // Add a submit handler to handle logic if certain fields are filled out.
  array_unshift($form['#submit'], 'feedback_form_submit');
}

function feedback_form_submit($form, &$form_state) {
  $form_state['redirect'] = 'node/2';
}

* Submit form and confirm not redirected per hook_form_alter() changes.

From my testing, webform forms will always have a null for $form_state['redirect'].

Proposed resolution

Since webform doesn't use the redirects value, we can add a is_null check before the redirect build linked above. If $form_state['redirects'] is null, build out message and url and override the redirect value. If redirect is populated, do nothing.

Note: This change will not support redirect setting in the hook_form_alter(). I didn't know this previously but $form_state['redirect'] is reset in drupal_build_form() in form.inc

if ($check_cache) {
      $uncacheable_keys = array_flip(array_diff(form_state_keys_no_cache(), array('always_process', 'temporary')));
      $form_state = array_diff_key($form_state, $uncacheable_keys);
      $form_state += $form_state_before_retrieval;
    }

Remaining tasks

testing

User interface changes

n/a

API changes

n/a

Data model changes

n/a

Release notes snippet

Support redirects via the $form_state['redirect'].