404: not existing event and courses shows white page instead of 404 msg
Summary
Steps to reproduce
https://openki.zuerich-lernt.ch/course/123 https://openki.zuerich-lernt.ch/event/foo
What is the current bug behavior?
just shows white page
What is the expected correct behavior?
It should show an error again, something like:
"maybe got deleted or never existed
if internal: try to log in..."