fix buf

Author: wxiaoguang

routers/web/repo/wiki.go

@@ -252,8 +252,8 @@ func renderViewPage(ctx *context.Context) (*git.Repository, *git.TreeEntry) {
 
 	rctx := renderhelper.NewRenderContextRepoWiki(ctx, ctx.Repo.Repository)
 
-	buf := &strings.Builder{}
 	renderFn := func(data []byte) (escaped *charset.EscapeStatus, output template.HTML, err error) {
+		buf := &strings.Builder{}
 		markupRd, markupWr := io.Pipe()
 		defer markupWr.Close()
 		done := make(chan struct{})