Merge pull request #12 from yangfasheng/master

update jerry_util.c

rtthread-port/jerry_util.c

@@ -73,6 +73,9 @@ jerry_value_t js_call_func_obj(const jerry_value_t func_obj_val, /**< function o
 {
     jerry_value_t ret;
 
+    if (_call_func_lock == RT_NULL)
+        return jerry_create_null();
+
     rt_mutex_take(_call_func_lock, RT_WAITING_FOREVER);
     ret = jerry_call_function(func_obj_val, this_val, args_p, args_count);
     rt_mutex_release(_call_func_lock);
@@ -252,6 +255,7 @@ extern int js_buffer_cleanup();
 int js_util_cleanup(void)
 {
     rt_mutex_delete(_call_func_lock);
+    _call_func_lock = RT_NULL;
 	
     js_buffer_cleanup();
     return 0;