Harshavardhana f234c35020 lock: slice length of lock clients should be precisely urls. (#3254)
This patch fixes a possible bug, reproduced rarely only seen
once.

```
panic: runtime error: index out of range

goroutine 136 [running]:
panic(0xac1a40, 0xc4200120b0)
    /usr/local/go/src/runtime/panic.go:500 +0x1a1
github.com/minio/minio/vendor/github.com/minio/dsync.lock.func1(0xc4203d2240, 0x4, 0xc420474080, 0x4, 0x4, 0xc4202abb60, 0x0, 0xa86d01, 0xefcfc0, 0xc420417a80)
    /go/src/github.com/minio/minio/vendor/github.com/minio/dsync/drwmutex.go:170 +0x69b
created by github.com/minio/minio/vendor/github.com/minio/dsync.lock
    /go/src/github.com/minio/minio/vendor/github.com/minio/dsync/drwmutex.go:191 +0xf4
```
2016-11-14 10:18:56 -08:00
..
2016-10-26 08:46:14 -07:00
2016-10-14 19:57:40 -07:00
2016-09-29 23:42:10 -07:00
2016-08-24 22:54:34 -07:00