chore: Update the value of sys.dialogue_count to start from 1. (#25905)

api/core/app/apps/advanced_chat/app_generator.py

             db.session.refresh(conversation)
 
         # get conversation dialogue count
-        self._dialogue_count = get_thread_messages_length(conversation.id)
+        # NOTE: dialogue_count should not start from 0,
+        # because during the first conversation, dialogue_count should be 1.
+        self._dialogue_count = get_thread_messages_length(conversation.id) + 1
 
         # init queue manager
         queue_manager = MessageBasedAppQueueManager(

api/services/workflow_service.py

         if workflow.type != WorkflowType.WORKFLOW.value:
             system_variable.query = query
             system_variable.conversation_id = conversation_id
-            system_variable.dialogue_count = 0
+            system_variable.dialogue_count = 1
     else:
         system_variable = SystemVariable.empty()