Adjust the logic added by #1246 (#1269)

Author: seratch

slack_sdk/socket_mode/builtin/internals.py

@@ -204,8 +204,6 @@ def receive(specific_buffer_size: Optional[int] = None):
         size = specific_buffer_size if specific_buffer_size is not None else receive_buffer_size
         with sock_receive_lock:
             received_bytes = sock.recv(size)
-            if not received_bytes:
-                raise ConnectionError("Connection is closed")
             if all_message_trace_enabled:
                 logger.debug(f"Received bytes: {received_bytes}")
             return received_bytes