[commands] Fix issue where Bot would raise if not given a description.
[commands] Fix issue where Bot would raise if not given a description.

Harmon758/discord.py,Theoretical/UselessBot,khazhyk/discord.py,jhgg/discord.py,mgardne8/discord.py,variablehair/Eggplantato,Rapptz/discord.py,imayhaveborkedit/discord.py,Harmon758/discord.py,lgkern/PriestPy,rapptz/discord.py