When the git repository on storage is changed, the repository modal should also be updated (#18088)

User would keep seeing an empty repo if:
* An error occurs during the first git pushing/receiving
* A user replaces the Gitea's empty repository manually
Fix: when a user is viewing the repository web page, if the repoModal.IsEmpty is true, we check the git repository again to detect whether it is really empty.

However: the IsEmpty flag is deeply broken and should be removed. For example it's possible for a repository to be non-empty by that flag but still 500 because there are no branches - only tags -or the default branch is non-extant as it has been 0-pushed.

routers/web/repo/view.go

@@ -840,9 +840,31 @@ func renderCode(ctx *context.Context) {
 	ctx.Data["PageIsViewCode"] = true
 
 	if ctx.Repo.Repository.IsEmpty {
+		reallyEmpty, err := ctx.Repo.GitRepo.IsEmpty()
+		if err != nil {
+			ctx.ServerError("GitRepo.IsEmpty", err)
+			return
+		}
+		if reallyEmpty {
 			ctx.HTML(http.StatusOK, tplRepoEMPTY)
 			return
 		}
+		// the repo is not really empty, so we should update the modal in database
+		// such problem may be caused by:
+		// 1) an error occurs during pushing/receiving.  2) the user replaces an empty git repo manually
+		// and even more: the IsEmpty flag is deeply broken and should be removed with the UI changed to manage to cope with empty repos.
+		// it's possible for a repository to be non-empty by that flag but still 500
+		// because there are no branches - only tags -or the default branch is non-extant as it has been 0-pushed.
+		ctx.Repo.Repository.IsEmpty = false
+		if err = repo_model.UpdateRepositoryCols(ctx.Repo.Repository, "is_empty"); err != nil {
+			ctx.ServerError("UpdateRepositoryCols", err)
+			return
+		}
+		if err = models.UpdateRepoSize(db.DefaultContext, ctx.Repo.Repository); err != nil {
+			ctx.ServerError("UpdateRepoSize", err)
+			return
+		}
+	}
 
 	title := ctx.Repo.Repository.Owner.Name + "/" + ctx.Repo.Repository.Name
 	if len(ctx.Repo.Repository.Description) > 0 {