Bug Report: Utils.is_instructor_of_this_course()

Hi,

I found this error in our development environment with debug log turned on. When the single course page is visited by users not logged in, the SQL in the function Utils.is_instructor_of_this_course($instructor_id=0, $course_id=0) is invalid, since the $instructor_id is false.

The statement
$instructor = $wpdb->get_col(”
SELECT umeta_id
FROM {$wpdb->usermeta}
WHERE user_id = {$instructor_id}
AND meta_key = ‘_tutor_instructor_course_id’
AND meta_value = {$course_id}
“);

causes error:
WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘AND meta_key = ‘_tutor_instructor_course_id’
AND meta_value = 783′ at line 4 for query
SELECT umeta_id
FROM xrv_usermeta
WHERE user_id =
AND meta_key = ‘_tutor_instructor_course_id’
AND meta_value = 783
made by require(‘wp-blog-header.php’), require_once(‘wp-includes/template-loader.php’), include(‘/plugins/tutor/templates/single-course.php’), tutor_course_enroll_box, TUTOR\Utils->is_instructor_of_this_course

I hope this error report can help you make the great Tutor LMS plugin even better.

Best regards,
Kooyaya