child_process: simplify send() result handling

PR-URL: https://github.com/nodejs/node/pull/13459
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

lib/internal/child_process.js

@@ -645,16 +645,15 @@ function setupChannel(target, channel) {
           obj.postSend(handle, options, target);
       }
 
-      req.oncomplete = function() {
-        if (this.async === true)
+      if (req.async) {
+        req.oncomplete = function() {
           control.unref();
-        if (typeof callback === 'function')
-          callback(null);
-      };
-      if (req.async === true) {
+          if (typeof callback === 'function')
+            callback(null);
+        };
         control.ref();
-      } else {
-        process.nextTick(function() { req.oncomplete(); });
+      } else if (typeof callback === 'function') {
+        process.nextTick(callback, null);
       }
     } else {
       // Cleanup handle on error