Error when you click "Try it" for a problem in a homework set not assigned to you.

[ionparticle]

This is for branch 2.5.2

To Reproduce

1. Create a homework set as a prof user, add some problems to it, then log out.
2. Log in as another prof user, go to the homework set and then click "Try it" for any of the problems.
3. Get an error like the screenshot here:
   

Workaround

Assigning the homework set to yourself fixes the issue.

Other Note

I brought this up on IRC a while ago, so not sure if a fix was actually committed and I'm just not finding it, previous discussions:

• http://irclog.perlgeek.de/webwork/2012-10-25#i_6100190
• http://irclog.perlgeek.de/webwork/2012-10-26