Prevent crash when showing scratchpad on new ws.

Fix #469

sway/commands.c

@@ -672,8 +672,9 @@ static void hide_view_in_scratchpad(swayc_t *sp_view) {
 	remove_child(sp_view);
 	if (swayc_active_workspace() != ws && ws->floating->length == 0 && ws->children->length == 0) {
 		destroy_workspace(ws);
-	}
+	} else {
 		arrange_windows(ws, -1, -1);
+	}
 	set_focused_container(container_under_pointer());
 }