`select last() from foo` causes panic

```
[11/11/14 15:42:57] [INFO] Start Query: db: dailymile, u: root, q: select last() from dgnorton.pace;
[11/11/14 15:42:57] [DEBG] Querying 3 shards for query
[11/11/14 15:42:57] [EROR] ********************************BUG********************************
Database: dailymile
Query: [select last() from dgnorton.pace;]
Error: runtime error: invalid memory address or nil pointer dereference. Stacktrace: goroutine 50 [running]:
github.com/influxdb/influxdb/common.RecoverFunc(0xc20802ca06, 0x9, 0xc2081c0870, 0x21, 0x0)
	/home/dgnorton/go/src/github.com/influxdb/influxdb/common/recover.go:14 +0xbb
github.com/influxdb/influxdb/engine.ProcessorChain(0x0, 0x0, 0x0, 0x0)
	/home/dgnorton/go/src/github.com/influxdb/influxdb/engine/processor.go:25 +0x4e
github.com/influxdb/influxdb/coordinator.(*Coordinator).getShardsAndProcessor(0xc2081004a0, 0xc20820e1e0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/home/dgnorton/go/src/github.com/influxdb/influxdb/coordinator/coordinator.go:246 +0x303
github.com/influxdb/influxdb/coordinator.(*Coordinator).runQuerySpec(0xc2081004a0, 0xc20820e1e0, 0x7ff5a9c342f8, 0xc20802e1b0, 0x0, 0x0)
	/home/dgnorton/go/src/github.com/influxdb/influxdb/coordinator/coordinator.go:294 +0x93
github.com/influxdb/influxdb/coordinator.(*Coordinator).runSingleQuery(0xc2081004a0, 0x7ff5a9c34260, 0xc2080fbb00, 0xc20802ca06, 0x9, 0xc2081c0de0, 0x7ff5a9c342f8, 0xc20802e1b0, 0x0, 0x0)
```