use EMPTY_STRING in _parent_via_in_reply_to
authorDavid Bremner <david@tethera.net>
Mon, 3 Sep 2018 15:26:10 +0000 (12:26 -0300)
committerDavid Bremner <david@tethera.net>
Thu, 6 Sep 2018 11:07:13 +0000 (08:07 -0300)
commitac2146118b83ca08aa6dd1275f65eefaed9fe2c0
treea140b6ea08bd1ca412ac561bee270c9822154b8b
parentb9d4eb04126c3ac4e7287443de7eae7290cd5273
use EMPTY_STRING in _parent_via_in_reply_to

This is a review suggestion [1] of Tomi. I decided not to squash it
so that the code movement remains clear.

[1]: id:m2pnxxgf5q.fsf@guru.guru-group.fi
lib/thread.cc