fix: clean manifest plugin state at build start (#3530)

Author: patak-dev

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

@@ -22,10 +22,15 @@ export interface ManifestChunk {
 export function manifestPlugin(config: ResolvedConfig): Plugin {
   const manifest: Manifest = {}
 
-  let outputCount = 0
+  let outputCount: number
 
   return {
     name: 'vite:manifest',
+
+    buildStart() {
+      outputCount = 0
+    },
+
     generateBundle({ format }, bundle) {
       function getChunkName(chunk: OutputChunk) {
         if (chunk.facadeModuleId) {