Fix missed return (#29450) (#29453)

Backport #29450 by @lunny

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/api/v1/repo/file.go

@@ -649,6 +649,7 @@ func UpdateFile(ctx *context.APIContext) {
 	apiOpts := web.GetForm(ctx).(*api.UpdateFileOptions)
 	if ctx.Repo.Repository.IsEmpty {
 		ctx.Error(http.StatusUnprocessableEntity, "RepoIsEmpty", fmt.Errorf("repo is empty"))
+		return
 	}
 
 	if apiOpts.BranchName == "" {