[dovecot/core] 979a13: lib: istream-multiplex - Minor optimization

[GitHub]

  Branch: refs/heads/master-2.2
  Home:   https://github.com/dovecot/core
  Commit: 979a1396a467dc5cbc26969067e8ac826a9dd747
      https://github.com/dovecot/core/commit/979a1396a467dc5cbc26969067e8ac826a9dd747
  Author: Timo Sirainen <timo.sirainen at dovecot.fi>
  Date:   2017-10-10 (Tue, 10 Oct 2017)

  Changed paths:
    M src/lib/istream-multiplex.c

  Log Message:
  -----------
  lib: istream-multiplex - Minor optimization

There's no need to find channel when we already know it. This also helps
static analyzers to understand that req_channel can't be NULL.