[dovecot/core] 0ac0c9: lib-smtp: command parser: Fix error recovery.

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 0ac0c93af1bb5c2aabf953bfebbd7df39665e080
      https://github.com/dovecot/core/commit/0ac0c93af1bb5c2aabf953bfebbd7df39665e080
  Author: Stephan Bosch <stephan.bosch at dovecot.fi>
  Date:   2017-12-18 (Mon, 18 Dec 2017)

  Changed paths:
    M src/lib-smtp/smtp-command-parser.c

  Log Message:
  -----------
  lib-smtp: command parser: Fix error recovery.

Input characters were not skipped upon error, meaning that error recovery would encounter these again.
This would make the parser parse the same data over and over again, yielding the same error.
This in turn caused the SMTP server application to hang in an infinite input loop, submitting error replies in the process, thereby filling up the process memory until exhaustion.
Problem seen in submission service, but LMTP is also affected.