Check if there is a built code (#5415)

index.js

@@ -1 +1,7 @@
-require('./built').default();
+const fs = require('fs');
+
+if (fs.existsSync('./built')) {
+	require('./built').default();
+} else {
+	console.log('Built code is not found. Probably an error occurred during a build or you just forgot to build.');
+}