added introductory prompt

backend.py

@@ -101,12 +101,6 @@ def handle_query(query_str: str,
     
     else:
         # The index is already built, no need to rebuild it.
-        pass    
-
-    try:
-          
-        memory = ChatMemoryBuffer.from_defaults(token_limit=None)
-        
         conversation: List[ChatMessage] = []
         for user, assistant in chat_history:
             conversation.extend(
@@ -117,6 +111,12 @@ def handle_query(query_str: str,
                 ]
             )
         #conversation.append( ChatMessage(role=MessageRole.USER, content=query_str))
+        pass    
+
+    try:
+          
+        memory = ChatMemoryBuffer.from_defaults(token_limit=None)
+        
         
         chat_engine = index.as_chat_engine(
         chat_mode="condense_plus_context",