Fix a infinite course flaw in the "Course Prerequisites" drop down of CourseInfo

[ollibowers]

• Certain plans will lead to certain courses displaying every other course as potential prerequisite
• This breaks the prereq tree greatly
• Find how to reproduce this and come up with an alternate response that describes the intended prereq satisfaction

Example:

• have COMP1511, COMP1521, COMP3211, COMP1911, COMP3131, COMP3121, COMP3151 planned
• check out MDIA3003 in course selector

Example:

• COMP1511, COMP1521, COMP2521, COMP1531, COMP3891, COMP2511 planned
• check out COMP3901

Appears to be related to the level requirements