Initialize BaseGroupChat before reset (#5608)

Fixes #5366 

Solution: Instead of raising an error called `_init()`

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Co-authored-by: Jack Gerrits <[email protected]>

python/packages/autogen-agentchat/src/autogen_agentchat/teams/_group_chat/_base_group_chat.py

@@ -494,7 +494,7 @@ async def main() -> None:
         """
 
         if not self._initialized:
-            raise RuntimeError("The group chat has not been initialized. It must be run before it can be reset.")
+            await self._init(self._runtime)
 
         if self._is_running:
             raise RuntimeError("The group chat is currently running. It must be stopped before it can be reset.")