fix(backend_server.py): check if client to disconnect has an open socket

src/judas_server/backend/backend_server.py

@@ -168,6 +168,12 @@ class BackendServer:
         """
         self.logger.info(f"[-] Disconnecting {client}...")
 
+        if client.socket is None:
+            self.logger.warning(
+                f"Client {client} has no socket, nothing to disconnect."
+            )
+            return
+
         try:
             self.selector.unregister(client.socket)
         except Exception as e: