Crawler doesn't crawl unless Read Message History perms are explicitly granted

[robstolarz]

Repro: point statbot at a guild containing channels that don't have Read Message History explicitly granted to a bot user. The crawler will ignore those channels.

Consider

statbot/statbot/crawler.py

Line 159 in 8113710

if channel.permissions_for(guild.me).read_message_history:

Replacing this conditional with True will cause the crawler to start indexing those channels again (although it will then fail on channels it can't read).