Command invocations which start with valid commands thrown unknown errors

[finnbar]

.sayblah will cause an "unknown error", while .cube (or another command that doesn't exist) will correctly complain that "No command with that name was found!".

[L0neGamer]

Additionally, typing .sayblah's results in no error at all, despite it being an invalid command.

One way to "fix" this is when the bot gets an invalid error, no error is sent at all. If the first suggestion from #9 is implemented, an error can be sent if an invalid command is requested to this kind of prefix.