Was made refactoring

Author: Taritsyn

src/JavaScriptEngineSwitcher.ChakraCore/ScriptDispatcher.cs

@@ -102,6 +102,7 @@ private void StartThread()
 						task = _taskQueue.Dequeue();
 						if (task == null)
 						{
+							_taskQueue.Clear();
 							return;
 						}
 					}
@@ -177,6 +178,11 @@ public T Invoke<T>(Func<T> func)
 		{
 			VerifyNotDisposed();
 
+			if (func == null)
+			{
+				throw new ArgumentNullException("func");
+			}
+
 			return (T)InnnerInvoke(() => func());
 		}
 
@@ -189,6 +195,11 @@ public void Invoke(Action action)
 		{
 			VerifyNotDisposed();
 
+			if (action == null)
+			{
+				throw new ArgumentNullException("action");
+			}
+
 			InnnerInvoke(() =>
 			{
 				action();
@@ -217,25 +228,17 @@ private void Dispose(bool disposing)
 			if (_disposedFlag.Set())
 			{
 				EnqueueTask(null);
-				_thread.Join();
 
-				if (_waitHandle != null)
+				if (_thread != null)
 				{
-					_waitHandle.Dispose();
-					_waitHandle = null;
+					_thread.Join();
+					_thread = null;
 				}
 
-				if (disposing)
+				if (_waitHandle != null)
 				{
-					lock (_taskQueueSynchronizer)
-					{
-						if (_taskQueue != null)
-						{
-							_taskQueue.Clear();
-						}
-					}
-
-					_thread = null;
+					_waitHandle.Dispose();
+					_waitHandle = null;
 				}
 			}
 		}