Only defer seat attachment during initial startup

Deferred commands are only run once, during sway startup. This means
that deferring seat attachment based on whether we are reading the
config prevents devices from being reattached to the correct seat during
a config reload. Instead, only defer if the config is not yet active.

Fixes #6048.

sway/commands/seat/attach.c

@@ -12,7 +12,7 @@ struct cmd_results *seat_cmd_attach(int argc, char **argv) {
 	if (!config->handler_context.seat_config) {
 		return cmd_results_new(CMD_FAILURE, "No seat defined");
 	}
-	if (config->reading) {
+	if (!config->active) {
 		return cmd_results_new(CMD_DEFER, NULL);
 	}