fix: pnpm dev時にファイルが空ならバックエンドの起動を待つように (#10210)

scripts/dev.js

@@ -40,8 +40,9 @@ const fs = require('fs');
 
 	const start = async () => {
 		try {
-			const exist = fs.existsSync(__dirname + '/../packages/backend/built/boot/index.js')
-			if (!exist) throw new Error('not exist yet');
+			const stat = fs.statSync(__dirname + '/../packages/backend/built/boot/index.js');
+			if (!stat) throw new Error('not exist yet');
+			if (stat.size === 0) throw new Error('not built yet');
 
 			await execa('pnpm', ['start'], {
 				cwd: __dirname + '/../',