nsq_to_nsq: index out of bounds

Not sure the cause of this yet but just started getting this.

```
2014/07/27 11:40:05 finished 25000 requests - 99th: 98.30ms - 95th: 5.96ms - avg: 6.74ms
panic: runtime error: index out of range

goroutine 34 [running]:
runtime.panic(0x6fc080, 0x8eb73c)
	/usr/local/Cellar/go/1.3/libexec/src/pkg/runtime/panic.c:279 +0xf5
main.percentile(0x4057c00000000000, 0xc208206000, 0x0, 0x7c00, 0x0, 0xc2080c8720)
	/Users/jehiah/projects/gopath/src/github.com/bitly/nsq/apps/nsq_to_nsq/nsq_to_nsq.go:288 +0x94
main.(*PublishHandler).responder(0xc208028cb0)
	/Users/jehiah/projects/gopath/src/github.com/bitly/nsq/apps/nsq_to_nsq/nsq_to_nsq.go:139 +0x616
created by main.main
	/Users/jehiah/projects/gopath/src/github.com/bitly/nsq/apps/nsq_to_nsq/nsq_to_nsq.go:394 +0xe5e
```