Fix markup init after issue comment editing (#35536) (#35537)

Backport #35536 by wxiaoguang

Fix #35533

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/issue_comment.go

@@ -9,12 +9,14 @@ import (
 	"html/template"
 	"net/http"
 	"strconv"
+	"strings"
 
 	issues_model "code.gitea.io/gitea/models/issues"
 	"code.gitea.io/gitea/models/renderhelper"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/gitrepo"
+	"code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/markup/markdown"
 	repo_module "code.gitea.io/gitea/modules/repository"
@@ -287,9 +289,10 @@ func UpdateCommentContent(ctx *context.Context) {
 			ctx.ServerError("RenderString", err)
 			return
 		}
-	} else {
-		contentEmpty := fmt.Sprintf(`<span class="no-content">%s</span>`, ctx.Tr("repo.issues.no_content"))
-		renderedContent = template.HTML(contentEmpty)
+	}
+
+	if strings.TrimSpace(string(renderedContent)) == "" {
+		renderedContent = htmlutil.HTMLFormat(`<span class="no-content">%s</span>`, ctx.Tr("repo.issues.no_content"))
 	}
 
 	ctx.JSON(http.StatusOK, map[string]any{