imap-hibernate: Log error when connect(imap-master) fails

It was previously logged only with info-level.

src/imap-hibernate/imap-client.c

@@ -223,6 +223,7 @@ static bool imap_client_try_move_back(struct imap_client *client)
 		return TRUE;
 	} else if (ret < 0) {
 		/* failed to connect to the imap-master socket */
+		i_error("Failed to unhibernate client: %s", error);
 		imap_client_destroy(&client, error);
 		return TRUE;
 	}