unintuitive behavior when using &nsq.Config{} 

I got this on Ubuntu 12.04, go 1.2

```
panic: non-positive interval for NewTicker

goroutine 141 [running]:
runtime.panic(0x815520, 0xc21010d230)
    /usr/local/go/src/pkg/runtime/panic.c:266 +0xb6
time.NewTicker(0x0, 0x3fd8a050fdd8d7f5)
    /usr/local/go/src/pkg/time/tick.go:22 +0x9f
github.com/bitly/go-nsq.(*Consumer).lookupdLoop(0xc21005a8c0)
    /tmp/godep/rev/2b/9a8b5edc036235580256e9a5e5f118a0025151/src/github.com/bitly/go-nsq/consumer.go:228 +0x6e
created by github.com/bitly/go-nsq.(*Consumer).ConnectToNSQLookupd
    /tmp/godep/rev/2b/9a8b5edc036235580256e9a5e5f118a0025151/src/github.com/bitly/go-nsq/consumer.go:216 +0x282
```

This is https://github.com/bitly/go-nsq/commit/2b9a8b5edc036235580256e9a5e5f118a0025151

I'm connecting to 8 nsqlookupd hosts (which might increase the chance of this happening)

I'm not setting config.lookupdPollInterval in my code.