fix: Handle empty course_overviews in get_courses_order_by function

cms/djangoapps/contentstore/views/course.py

@@ -621,6 +621,8 @@ def get_courses_order_by(order_query, course_overviews):
         order_query (str): any string used to order Course Overviews.
         course_overviews (Course Overview objects): queryset to be ordered.
     """
+    if not course_overviews:
+        return []
     if not order_query:
         return course_overviews
     try: