[dovecot/core] c3d3fa: auth: Fix auth-policy crash when username is NULL

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: c3d3faa4f72a676e183f34be960cff13a5a725ae
      https://github.com/dovecot/core/commit/c3d3faa4f72a676e183f34be960cff13a5a725ae
  Author: Aki Tuomi <aki.tuomi at dovecot.fi>
  Date:   2016-11-23 (Wed, 23 Nov 2016)

  Changed paths:
    M src/auth/auth-policy.c

  Log Message:
  -----------
  auth: Fix auth-policy crash when username is NULL

If SASL request is invalid, or incomplete, and username
is left NULL, handle it gracefully by adding just
NUL byte in auth policy digest for username.