fix(css): remove empty css chunks with cssCodeSplit: false

Resolves #16582

When setting `cssCodeSplit: false` the styles are still split into one style file.
But currently the imported CSS results in empty chunks,
as in the current implementation empty chunks are only removed when `cssCodeSplit` was set to `true`.
So this also adds empty style chunks to `pureCSSChunks` even with `cssCodeSplit: false`.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

Author: susnux

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

@@ -723,13 +723,12 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
       }
 
       if (chunkCSS) {
+        if (isPureCssChunk && (opts.format === 'es' || opts.format === 'cjs')) {
+          // this is a shared CSS-only chunk that is empty.
+          pureCssChunks.add(chunk)
+        }
         if (config.build.cssCodeSplit) {
           if (opts.format === 'es' || opts.format === 'cjs') {
-            if (isPureCssChunk) {
-              // this is a shared CSS-only chunk that is empty.
-              pureCssChunks.add(chunk)
-            }
-
             const isEntry = chunk.isEntry && isPureCssChunk
             const cssFullAssetName = ensureFileExt(chunk.name, '.css')
             // if facadeModuleId doesn't exist or doesn't have a CSS extension,