Revision 4854

backport (glarose): Make sure that something gets passed to
renderProblems() for the userSet even when a global set is being edited
and it isn't assigned to any users. Gets rid of "odd number of elements
in hash assignment" errors in renderProblems. Because renderProblems
plugs in a fake set if it gets a false value in for the userSet, sending
in '' appears to solve the problem.