Panic if oper-classes title information is left blank

[erikh]

My config:

oper-classes:
   "foo":
     title:

error:

panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
github.com/ergochat/ergo/irc.(*Config).OperatorClasses(0xc0001ba400, 0xc0002b6300, 0xc, 0xc00023c8b8)
        /go/src/github.com/ergochat/ergo/irc/config.go:757 +0xaf6
github.com/ergochat/ergo/irc.LoadConfig(0xc000178177, 0x9, 0x9c4ee4, 0x6, 0xc00014b048)
        /go/src/github.com/ergochat/ergo/irc/config.go:1425 +0xe5e
main.main()
        /go/src/github.com/ergochat/ergo/ergo.go:146 +0x7c5

problem is the [0] in the title here:

https://github.com/ergochat/ergo/blob/stable/irc/config.go#L757