Merge 2 conditions into 1 for clarity

I was really confused with issue events and note events. If we want to use event.noteable_author_id then it should be event.note?. We can see that event.new_entity? would be called twice if it's a new issue.

We might want to abstract this away but at least this can make the dependency more clear.

We can see confusion at: !51 (comment 485232856)