Fix type check for server proc on mcp teardown

Author: Bas Alberts

main.py

@@ -208,7 +208,7 @@ async def mcp_session_task(
                     logging.debug(f"Starting cleanup for mcp server: {server._name}")
                     await server.cleanup()
                     logging.debug(f"Cleaned up mcp server: {server._name}")
-                    if server_proc:
+                    if server_proc is not None:
                         server_proc.stop()
                         try:
                             await asyncio.to_thread(server_proc.join_and_raise)