Sometimes finalizer for closing cluster happens panic

[bluele]

Hi, @khaf .

Client version: v1.27.0 (1dc8cf2).
Server version: Aerospike Server CE :3.14.0

Sometimes happens panic occasionally when the Close function is called multiple times in parallel.
It seems that closing tendChannel is called twice.

Sample code is here:

func main() {
	client, err := aerospike.NewClient("127.0.0.1", 3000)
	panicOnError(err)
        defer client.Close()
        Task(client)
        // end
}

Traceback is here: (file path is simplified)

panic: close of closed channel
goroutine 4 [running]:
vendor/github.com/aerospike/aerospike-client-go.(*Cluster).Close(0xc42007afc0)
vendor/github.com/aerospike/aerospike-client-go/cluster.go:898 +0x5c
vendor/github.com/aerospike/aerospike-client-go.(*Client).Close(0xc42036b410)
vendor/github.com/aerospike/aerospike-client-go/client.go:109 +0x2e
vendor/github.com/aerospike/aerospike-client-go.clientFinalizer(0xc42036b410)
vendor/github.com/aerospike/aerospike-client-go/client.go:54 +0x2b