[tasks] Allow Loop.cancel in Loop.before_loop
[tasks] Allow Loop.cancel in Loop.before_loop

Task cancel raises on the next awaited coro, so I've added this 0-sleep "hack"

I'm internally debating if leaving the comment there, but I'm sure it would confuse the uninformed of this trick.
rapptz/discord.py,Rapptz/discord.py,Harmon758/discord.py,Harmon758/discord.py,khazhyk/discord.py