fix(ampy): 添加 dispose 方法 null 检查防止重复调用报错

mixly/common/modules/mixly-modules/web/ampy.js

@@ -417,12 +417,16 @@ class AmpyExt extends Ampy {
 
         async dispose() {
             this.#active_ = false;
+            if (this.#device_) {
                 await this.#device_.dispose();
                 this.#device_ = null;
+            }
+            if (this.#events_) {
                 this.#events_.reset();
                 this.#events_ = null;
             }
         }
+    }
 
     Web.Ampy = AmpyExt;