Check "Manage Staff" NetID string for appropriate length

[wadefagen]

Reproduce:

• Click a course
• Click "Manage Staff"
• Add really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_really_long_netid_that_should_never_exist_
• See error message.