[dovecot/core] 4a1e2e: doveadm: Unref header search context after use

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 4a1e2e8e85ad5d4ab43496a5f3cd6b7ff6ac5955
      https://github.com/dovecot/core/commit/4a1e2e8e85ad5d4ab43496a5f3cd6b7ff6ac5955
  Author: Aki Tuomi <aki.tuomi at dovecot.fi>
  Date:   2017-12-29 (Fri, 29 Dec 2017)

  Changed paths:
    M src/doveadm/doveadm-mail-iter.c

  Log Message:
  -----------
  doveadm: Unref header search context after use

Fixes memory leak, found by valgrind