Fix validity of the FROM email address not being checked (#29347) (#29360)

Backport #29347 by @carlosfelgueiras

Fixes #27188.
Introduces a check on the installation that tries to parse the FROM
address. If it fails, shows a new error message to the user.

Co-authored-by: Carlos Felgueiras <carlosfelgueiras@tecnico.ulisboa.pt>
Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

options/locale/locale_en-US.ini

@@ -246,6 +246,7 @@ email_title = Email Settings
 smtp_addr = SMTP Host
 smtp_port = SMTP Port
 smtp_from = Send Email As
+smtp_from_invalid = The "Send Email As" address is invalid
 smtp_from_helper = Email address Gitea will use. Enter a plain email address or use the "Name" <email@example.com> format.
 mailer_user = SMTP Username
 mailer_password = SMTP Password

routers/install/install.go

@@ -7,6 +7,7 @@ package install
 import (
 	"fmt"
 	"net/http"
+	"net/mail"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -417,6 +418,11 @@ func SubmitInstall(ctx *context.Context) {
 	}
 
 	if len(strings.TrimSpace(form.SMTPAddr)) > 0 {
+		if _, err := mail.ParseAddress(form.SMTPFrom); err != nil {
+			ctx.RenderWithErr(ctx.Tr("install.smtp_from_invalid"), tplInstall, &form)
+			return
+		}
+
 		cfg.Section("mailer").Key("ENABLED").SetValue("true")
 		cfg.Section("mailer").Key("SMTP_ADDR").SetValue(form.SMTPAddr)
 		cfg.Section("mailer").Key("SMTP_PORT").SetValue(form.SMTPPort)