[dovecot/core] e591a3: lib-mail: Fix message_part_data_is_plain_7bit()

[GitHub]

  Branch: refs/heads/master-2.2
  Home:   https://github.com/dovecot/core
  Commit: e591a396fb59b147ea5828e271512cb7af483a8e
      https://github.com/dovecot/core/commit/e591a396fb59b147ea5828e271512cb7af483a8e
  Author: Timo Sirainen <timo.sirainen at dovecot.fi>
  Date:   2017-02-22 (Wed, 22 Feb 2017)

  Changed paths:
    M src/lib-mail/message-part-data.c

  Log Message:
  -----------
  lib-mail: Fix message_part_data_is_plain_7bit()

Content-Type parameters weren't handled exactly right.
Broken by recent changes.