ssr: fix json bundle path (fix #5037)

src/server/create-bundle-renderer.js

@@ -43,9 +43,10 @@ export function createBundleRendererCreator (createRenderer: () => Renderer) {
       path.isAbsolute(bundle)
     ) {
       if (fs.existsSync(bundle)) {
+        const isJSON = /\.json$/.test(bundle)
         basedir = basedir || path.dirname(bundle)
         bundle = fs.readFileSync(bundle, 'utf-8')
-        if (/\.json$/.test(bundle)) {
+        if (isJSON) {
           try {
             bundle = JSON.parse(bundle)
           } catch (e) {