sort package may return without waiting for children

panic: send on closed channel

goroutine 3562486 [running]:

runtime.gopanic(0xc7a520, 0xc237379b00)

        /usr/local/go/src/runtime/panic.go:425 +0x2a3 fp=0xc24dc91e50 sp=0xc24dc91de8

runtime.chansend(0xc7bc20, 0xc22ad90960, 0xc24dc91f4f, 0x1405801, 0xadfa5a, 0x8)

        /usr/local/go/src/runtime/chan.go:131 +0x1a3 fp=0xc24dc91ef8 sp=0xc24dc91e50

runtime.chansend1(0xc7bc20, 0xc22ad90960, 0xc24dc91f4f)

        /usr/local/go/src/runtime/chan.go:68 +0x43 fp=0xc24dc91f30 sp=0xc24dc91ef8

github.com/couchbase/query/sort.notify(0xc22ad90960)

        /home/couchbase/jenkins/workspace/watson-unix/goproj/src/github.com/couchbase/query/sort/sort.go:214 +0x4a fp=0xc24dc91f58 sp=0xc24dc91f30

github.com/couchbase/query/sort.quickSort(0x7f252c60d350, 0xc20a80ab00, 0x203, 0x20a, 0xc, 0xc22ad90960)

        /home/couchbase/jenkins/workspace/watson-unix/goproj/src/github.com/couchbase/query/sort/sort.go:210 +0x314 fp=0xc24dc91fb0 sp=0xc24dc91f58

runtime.goexit()

        /usr/local/go/src/runtime/asm_amd64.s:2232 +0x1 fp=0xc24dc91fb8 sp=0xc24dc91fb0

created by github.com/couchbase/query/sort.quickSort

        /home/couchbase/jenkins/workspace/watson-unix/goproj/src/github.com/couchbase/query/sort/sort.go:193 +0x248