Cannot add user from the group submenu

[bbibeault]

Zenoss's Admin -> User console has the ability to add users and add groups. It also has the ability to add users from the groups sub-menu. When you try and add a user with a custom group created, you receive an error.

Reproduce :

• Login as an admin user, go to Management -> Settings -> Users
• Add a custom group (name is not important)
• From the groups sub-menu, select "Add User"

Results :
Error submission page -

 Type: UnboundLocalError
Value: local variable 'groupid' referenced before assignment

Traceback (innermost last):

    * Module ZPublisher.Publish, line 114, in publish
    * Module ZPublisher.mapply, line 88, in mapply
    * Module ZPublisher.Publish, line 40, in call_object
    * Module Products.ZenModel.UserSettings, line 371, in manage_addUsersToGroups

UnboundLocalError: local variable 'groupid' referenced before assignment 

[bedwards]

patch submitted by my friend Leo, I verified it, but I'll get a code read before I check it in

[bedwards]

(In [10642]) Fixes #3658: print an error message when no groups are selected. fix by leo. reviewed by kells.