tls-autodetect: avoid a goroutine leak on timeout

prototypes/tls-autodetect.go

@@ -322,7 +322,7 @@ func prepare(client *client) {
 
 	// The Cgo resolver doesn't pthread_cancel getnameinfo threads, so not
 	// bothering with pointless contexts.
-	ch := make(chan string)
+	ch := make(chan string, 1)
 	go func() {
 		defer close(ch)
 		if names, err := net.LookupAddr(host); err != nil {