[dovecot/core] 909764: acl: Fix compiler warning

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 9097643138acfe54597f97549c8d9b4f4161aa07
      https://github.com/dovecot/core/commit/9097643138acfe54597f97549c8d9b4f4161aa07
  Author: Timo Sirainen <timo.sirainen at dovecot.fi>
  Date:   2016-11-28 (Mon, 28 Nov 2016)

  Changed paths:
    M src/plugins/acl/acl-backend.c

  Log Message:
  -----------
  acl: Fix compiler warning