logstash-input-journald crashes forever on bad message

[runesl]

I don't know how the bad message occured, but it causes the journald input plugin to go into restart loop. A more desirable behaviour would be to drop the message and continue.

  Error: Bad message
[2017-08-30T11:23:04,720][ERROR][logstash.pipeline        ] A plugin had an unrecoverable error. Will restart this plugin.
  Plugin: <LogStash::Inputs::Journald lowercase=>true, seekto=>"head", thisboot=>true, type=>"systemd", tags=>["miner"], id=>"029a27f623922b1d28cce96e23f3629f1578b0f2-1", enable_metric=>true, codec=><LogStash::Codecs::Plain id=>"plain_7ed02ee8-0a28-4ecb-96d6-f7643cd12e76", enable_metric=>true, charset=>"UTF-8">, threads=>1, flags=>0, path=>"/var/log/journal", filter=>{:_boot_id=>"4f55d1c32b484c76acb0cf9b24cad083"}, sincedb_write_interval=>15, wait_timeout=>3000000>
  Error: Bad message
[2017-08-30T11:23:05,726][ERROR][logstash.pipeline        ] A plugin had an unrecoverable error. Will restart this plugin.
  Plugin: <LogStash::Inputs::Journald lowercase=>true, seekto=>"head", thisboot=>true, type=>"systemd", tags=>["miner"], id=>"029a27f623922b1d28cce96e23f3629f1578b0f2-1", enable_metric=>true, codec=><LogStash::Codecs::Plain id=>"plain_7ed02ee8-0a28-4ecb-96d6-f7643cd12e76", enable_metric=>true, charset=>"UTF-8">, threads=>1, flags=>0, path=>"/var/log/journal", filter=>{:_boot_id=>"4f55d1c32b484c76acb0cf9b24cad083"}, sincedb_write_interval=>15, wait_timeout=>3000000>
  Error: Bad message

[matthew-hollick]

We have recently been hit by this issue in production.
Happy to help test the PR.
Is there anything stopping this being merged?