Ensure that IsManageableRoleGroupType only returns true for valid roles

IsManageableRoleGroupType was only checking that the role group was not
an ACL-only group -- not that it was also a valid group at all.  This
caused the queue watcher page to report "No valid Type specified" for
every user search result that was left blank.

Fixes: #29993
Merge branch '4.2/queue-watcher-valid-type' into 4.2-trunk