Lecture creation for course editors broken on course edit page

[fosterfarrell9]

The following bug in production was reported by a user: If you are a course editor and try to create a new lecture on the courses#edit page
(using the "plus" button), nothing happens when actually a modal should open. This is probably an error that comes from the voucher PR, we might have missed this dialogue back then. I guess it has not been noticed until now because most editors create new lectutres directly on the admin main page (where it works)