MDL-71392 mod_quiz: don't display grade to pass if not set.

mod/quiz/tests/behat/info_page.feature

@@ -30,3 +30,13 @@ Feature: Display of information before starting a quiz
       | TF1      | 1    |
     When I am on the "Quiz 1" "mod_quiz > View" page logged in as "student"
     Then I should see "Grade to pass: 60.00 out of 100.00"
+
+  Scenario: Check the pass grade is not displayed if not set
+    Given the following "activities" exist:
+      | activity   | name   | intro              | course | idnumber | gradepass |
+      | quiz       | Quiz 1 | Quiz 1 description | C1     | quiz1    |           |
+    And quiz "Quiz 1" contains the following questions:
+      | question | page |
+      | TF1      | 1    |
+    When I am on the "Quiz 1" "mod_quiz > View" page logged in as "student"
+    Then I should not see "Grade to pass: 0.00"

mod/quiz/view.php

@@ -187,7 +187,8 @@ if ($quiz->attempts != 1) {
             quiz_get_grading_option_name($quiz->grademethod));
 }
 
-if ($item && $item->gradepass) {
+// Inform user of the grade to pass if non-zero.
+if ($item && grade_floats_different($item->gradepass, 0)) {
     $a = new stdClass();
     $a->grade = quiz_format_grade($quiz, $item->gradepass);
     $a->maxgrade = quiz_format_grade($quiz, $quiz->grade);