Discard null sequences in the gateway.
Discard null sequences in the gateway.

This was forbidding the Discord gateway from allowing us to RESUME
properly, causing an over-abundance of READY being called.

Harmon758/discord.py,mgardne8/discord.py,rapptz/discord.py,Harmon758/discord.py,variablehair/Eggplantato,imayhaveborkedit/discord.py,khazhyk/discord.py,Rapptz/discord.py