- prevent create reop on existed path

- fix update lable break connection with repository

- create new label

- fix isRead check
- fix paging

If users are added to gogs due a reverse proxy automatically, their password is
set to their initial username. If their username is shorter than 6 characters,
they can never set a password. But since this password is required for some
operations (e.g. repository deletion), they could not use all features of gogs
until now.