Bugfix: Apply notify/register mail flags during install load (#37120)

`LoadSettingsForInstall` only ran `loadMailerFrom`, not
_loadRegisterMailFrom_ or _loadNotifyMailFrom_, so
Service.RegisterEmailConfirm and Service.EnableNotifyMail were never
read from app.ini on the install page.

Full startup runs those through loadMailsFrom; the install path was a
narrower subset and never included that step—an oversight from when
install-specific loading was added

Fixes #37112

modules/setting/setting.go

@@ -232,7 +232,7 @@ func LoadSettings() {
 func LoadSettingsForInstall() {
 	loadDBSetting(CfgProvider)
 	loadServiceFrom(CfgProvider)
-	loadMailerFrom(CfgProvider)
+	loadMailsFrom(CfgProvider)
 }
 
 var configuredPaths = make(map[string]string)