src: fix cardreader thread synchronization

- Make sure while handling AsyncResult in HandleReaderStatusChange
  (JS thread), the AsyncResult is not overwritten in HandlerFunction
  (SCardGetStatusChange thread).

src/cardreader.cpp

@@ -310,13 +310,13 @@ NAN_METHOD(CardReader::Close) {
         } while (uv_cond_timedwait(&obj->m_cond, &obj->m_mutex, 10000000) != 0);
     }
 
+    assert(uv_thread_join(&obj->m_status_thread) == 0);
+    obj->m_status_thread = 0;
+
     uv_mutex_unlock(&obj->m_mutex);
     uv_mutex_destroy(&obj->m_mutex);
     uv_cond_destroy(&obj->m_cond);
 
-    assert(uv_thread_join(&obj->m_status_thread) == 0);
-    obj->m_status_thread = 0;
-
     info.GetReturnValue().Set(Nan::New<Number>(result));
 }
 
@@ -325,6 +325,12 @@ void CardReader::HandleReaderStatusChange(uv_async_t *handle, int status) {
     Nan::HandleScope scope;
 
     AsyncBaton* async_baton = static_cast<AsyncBaton*>(handle->data);
+    CardReader* reader = async_baton->reader;
+
+    if (reader->m_status_thread) {
+        uv_mutex_lock(&reader->m_mutex);
+    }
+
     AsyncResult* ar = async_baton->async_result;
 
     if (ar->do_exit) {
@@ -336,9 +342,7 @@ void CardReader::HandleReaderStatusChange(uv_async_t *handle, int status) {
         };
 
         Nan::MakeCallback(async_baton->reader->handle(), "emit", 1, argv);
-        return;
-    }
-
+    } else {
         if (ar->result == SCARD_S_SUCCESS) {
             const unsigned argc = 3;
             Local<Value> argv[argc] = {
@@ -355,6 +359,11 @@ void CardReader::HandleReaderStatusChange(uv_async_t *handle, int status) {
             Local<Value> argv[argc] = { err };
             Nan::Callback(Nan::New(async_baton->callback)).Call(argc, argv);
         }
+    }
+
+    if (reader->m_status_thread) {
+        uv_mutex_unlock(&reader->m_mutex);
+    }
 }
 
 void CardReader::HandlerFunction(void* arg) {