Redirect from `{repo}/issues/new` to `{repo}/issues/new/choose` when blank issues are disabled (#26813) (#26847)

Backport #26813 by @JakobDev

You can currently visit `{repo}/issues/new` and create a blank issue,
even if it's disabled. This PR fixes this,

Fixes https://codeberg.org/forgejo/forgejo/issues/1356

Co-authored-by: JakobDev <jakobdev@gmx.de>

routers/web/repo/issue.go

@@ -877,9 +877,17 @@ func setTemplateIfExists(ctx *context.Context, ctxDataKey string, possibleFiles
 
 // NewIssue render creating issue page
 func NewIssue(ctx *context.Context) {
+	issueConfig, _ := issue_service.GetTemplateConfigFromDefaultBranch(ctx.Repo.Repository, ctx.Repo.GitRepo)
+	hasTemplates := issue_service.HasTemplatesOrContactLinks(ctx.Repo.Repository, ctx.Repo.GitRepo)
+	if !issueConfig.BlankIssuesEnabled && hasTemplates {
+		// The "issues/new" and "issues/new/choose" share the same query parameters "project" and "milestone", if blank issues are disabled, just redirect to the "issues/choose" page with these parameters.
+		ctx.Redirect(fmt.Sprintf("%s/issues/new/choose?%s", ctx.Repo.Repository.Link(), ctx.Req.URL.RawQuery), http.StatusSeeOther)
+		return
+	}
+
 	ctx.Data["Title"] = ctx.Tr("repo.issues.new")
 	ctx.Data["PageIsIssueList"] = true
-	ctx.Data["NewIssueChooseTemplate"] = issue_service.HasTemplatesOrContactLinks(ctx.Repo.Repository, ctx.Repo.GitRepo)
+	ctx.Data["NewIssueChooseTemplate"] = hasTemplates
 	ctx.Data["PullRequestWorkInProgressPrefixes"] = setting.Repository.PullRequest.WorkInProgressPrefixes
 	title := ctx.FormString("title")
 	ctx.Data["TitleQuery"] = title