fix(Permission): 修复后台权限注解解析逻辑 (#492)

- 无需权限验证的接口，可不写 Permission 注解

app/Http/Admin/Middleware/PermissionMiddleware.php

@@ -53,7 +53,8 @@ private function check(Dispatched $dispatched): bool
          */
         $permissions = [];
         $classAnnotation && $permissions[] = $classAnnotation;
-        $permissions[] = Arr::get($annotations, Permission::class);
+        $methodPermission = Arr::get($annotations, Permission::class);
+        $methodPermission && $permissions[] = $methodPermission;
         foreach ($permissions as $permission) {
             $this->handlePermission($permission);
         }