MDL-86810 completion: update module completion data correctly.

Ensure we check the correct field to determine form value.

course/modlib.php

@@ -625,7 +625,7 @@ function update_moduleinfo($cm, $moduleinfo, $course, $mform = null) {
         if (!empty($moduleinfo->completionunlocked)) {
             $cm->completion = $moduleinfo->completion;
             $cm->completionpassgrade = $moduleinfo->completionpassgrade ?? 0;
-            if ($moduleinfo->completiongradeitemnumber === '') {
+            if (empty($moduleinfo->completionusegrade)) {
                 $cm->completiongradeitemnumber = null;
             } else {
                 $cm->completiongradeitemnumber = $moduleinfo->completiongradeitemnumber;

course/tests/courselib_test.php

@@ -550,6 +550,7 @@ final class courselib_test extends advanced_testcase {
         // Completion common to all module.
         $moduleinfo->completion = COMPLETION_TRACKING_AUTOMATIC;
         $moduleinfo->completionview = COMPLETION_VIEW_REQUIRED;
+        $moduleinfo->completionusegrade = 1;
         $moduleinfo->completiongradeitemnumber = 1;
         $moduleinfo->completionpassgrade = 0;
         $moduleinfo->completionexpected = time() + (7 * 24 * 3600);