Fix crash on post editing and other events
Fix crash on post editing and other events

Tagging @tradingpost in an edit will make it crash, since edits have no
'user' property (https://api.slack.com/events/file_comment_edited).

Other events which don't have that property should also cause this issue.

Fix: ignore messages without 'user' property.

torgeirl/tradingpost,torgeirl/tradingpost-beepboop