Refactor tag completion handling into one function
diff --git a/src/node/ext/completion_queue_threadpool.cc b/src/node/ext/completion_queue_threadpool.cc
index 1917074..7b1bdda 100644
--- a/src/node/ext/completion_queue_threadpool.cc
+++ b/src/node/ext/completion_queue_threadpool.cc
@@ -148,9 +148,7 @@
   Nan::HandleScope scope;
   current_threads -= 1;
   TryAddWorker();
-  Nan::Callback *callback = GetTagCallback(result.tag);
-  Local<Value> argv[] = {Nan::Null(), GetTagNodeValue(result.tag)};
-  callback->Call(2, argv);
+  CompleteTag(result.tag, NULL);
 
   DestroyTag(result.tag);
 }
@@ -159,10 +157,7 @@
   Nan::HandleScope scope;
   current_threads -= 1;
   TryAddWorker();
-  Nan::Callback *callback = GetTagCallback(result.tag);
-  Local<Value> argv[] = {Nan::Error(ErrorMessage())};
-
-  callback->Call(1, argv);
+  CompleteTag(result.tag, ErrorMessage());
 
   DestroyTag(result.tag);
 }