Merge branch 'MDL-39761-MOODLE_23_STABLE' of https://github.com/lucisgit/moodle into MOODLE_23_STABLE

mod/assign/locallib.php

@@ -2662,7 +2662,9 @@ class assign {
             // Give each submission plugin a chance to process the submission
             $plugins = $this->get_submission_plugins();
             foreach ($plugins as $plugin) {
-                $plugin->submit_for_grading();
+                if ($plugin->is_enabled() && $plugin->is_visible()) {
+                    $plugin->submit_for_grading();
+                }
             }
 
             $submission->status = ASSIGN_SUBMISSION_STATUS_SUBMITTED;
@@ -2943,7 +2945,7 @@ class assign {
             $allempty = true;
             $pluginerror = false;
             foreach ($this->submissionplugins as $plugin) {
-                if ($plugin->is_enabled()) {
+                if ($plugin->is_enabled() && $plugin->is_visible()) {
                     if (!$plugin->save($submission, $data)) {
                         $notices[] = $plugin->get_error();
                         $pluginerror = true;