gopkg.in-ldap.v2: Authentication bypass via empty password

In the ldap.v2 (aka go-ldap) package through 2.5.0 for Go, an attacker may be able to login with an empty password. This issue affects an application using this package if these conditions are met: (1) it relies only on the return error of the Bind function call to determine whether a user is authorized (i.e., a nil return value is interpreted as successful authorization) and (2) it is used with an LDAP server allowing unauthenticated bind.