提前初始化updatelist，fix找不找变量的问题

backend/SystemUpdater/UpdateManager.py

@@ -199,6 +199,8 @@ class UpdateManager():
             _success = False
             return _success,header,desc
             
+        self.update_list = UpdateList(self)
+
         #更新important.list
         if self.options.no_update_source is False:
             _success,header,desc = self.dbusController._on_update_important_list()
@@ -210,7 +212,6 @@ class UpdateManager():
         if _success == False:
             return _success,header,desc
 
-        self.update_list = UpdateList(self)
         try:
             _success,header,desc = self.update_list.update(self.cache)
         except SystemError as e: