chore: form binding trim space (#38978)

Use "binding:TrimSpace" instead of fragile IsEmptyString

And fix a bug in locale's `HasKey`: it should also try the default
language if current language doesn't have the translation key, a new
test is added.

routers/web/admin/auths.go

@@ -18,7 +18,6 @@ import (
 	"gitea.dev/modules/log"
 	"gitea.dev/modules/setting"
 	"gitea.dev/modules/templates"
-	"gitea.dev/modules/util"
 	"gitea.dev/modules/web"
 	auth_service "gitea.dev/services/auth"
 	"gitea.dev/services/auth/source/ldap"
@@ -210,7 +209,7 @@ func parseOAuth2Config(form forms.AuthenticationForm) *oauth2.Source {
 }
 
 func parseSSPIConfig(ctx *context.Context, form forms.AuthenticationForm) (*sspi.Source, error) {
-	if util.IsEmptyString(form.SSPISeparatorReplacement) {
+	if form.SSPISeparatorReplacement == "" {
 		ctx.Data["Err_SSPISeparatorReplacement"] = true
 		return nil, errors.New(ctx.Locale.TrString("form.require_error", ctx.Locale.TrString("form.SSPISeparatorReplacement")))
 	}