perf(css): only replace empty chunk if imported (#16349)

Author: bluwy

packages/vite/src/node/plugins/css.ts

@@ -860,6 +860,7 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
         for (const file in bundle) {
           const chunk = bundle[file]
           if (chunk.type === 'chunk') {
+            let chunkImportsPureCssChunk = false
             // remove pure css chunk from other chunk's imports,
             // and also register the emitted CSS files under the importer
             // chunks instead.
@@ -874,11 +875,14 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
                 importedAssets.forEach((file) =>
                   chunk.viteMetadata!.importedAssets.add(file),
                 )
+                chunkImportsPureCssChunk = true
                 return false
               }
               return true
             })
-            chunk.code = replaceEmptyChunk(chunk.code)
+            if (chunkImportsPureCssChunk) {
+              chunk.code = replaceEmptyChunk(chunk.code)
+            }
           }
         }