Fix double hashing of shared link passwords

The plain text password for a shared links was hashed and, then, the
hashed password was hashed again and set as the final password. Due to
this the password introduced in the "Authenticate" page for the shared
link was always a wrong password, and thus the file could not be
accessed.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>