Allow HOST has no port (#22280)

Fix #22274

This PR will allow `HOST` without port. Then a default port will be
given in future steps.

modules/setting/mailer_test.go

@@ -0,0 +1,43 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	ini "gopkg.in/ini.v1"
+)
+
+func TestParseMailerConfig(t *testing.T) {
+	iniFile := ini.Empty()
+	kases := map[string]*Mailer{
+		"smtp.mydomain.com": {
+			SMTPAddr: "smtp.mydomain.com",
+			SMTPPort: "465",
+		},
+		"smtp.mydomain.com:123": {
+			SMTPAddr: "smtp.mydomain.com",
+			SMTPPort: "123",
+		},
+		":123": {
+			SMTPAddr: "127.0.0.1",
+			SMTPPort: "123",
+		},
+	}
+	for host, kase := range kases {
+		t.Run(host, func(t *testing.T) {
+			iniFile.DeleteSection("mailer")
+			sec := iniFile.Section("mailer")
+			sec.NewKey("ENABLED", "true")
+			sec.NewKey("HOST", host)
+
+			// Check mailer setting
+			parseMailerConfig(iniFile)
+
+			assert.EqualValues(t, kase.SMTPAddr, MailService.SMTPAddr)
+			assert.EqualValues(t, kase.SMTPPort, MailService.SMTPPort)
+		})
+	}
+}