Userlist: async load doesnt fill checked group/subadmin array

i found that when removeing a group to an user async loaded in the javascript console give an error and the group wasnt removed.After a little of reserch i found that in case of async userlist load from 31th user going on oc aspect to have an array inside element.checked but it found a string ( instead for server side loaded user it found an array) and when it try to push or splice it give and error 
https://github.com/owncloud/core/issues/9610
ps . i tryed to be as clear as possible for my poor english skill :D 

the alternative is to use `_.isString()`