Refactor CultureInfo validation logic in validators

Author: KrzysztofPajak

src/Web/Grand.Web.Admin/Validators/Directory/CurrencyValidator.cs

@@ -37,10 +37,9 @@ public CurrencyValidator(
                 {
                     if (string.IsNullOrEmpty(x))
                         return true;
-                    //create a CultureInfo object
-                    //if "DisplayLocale" is wrong, then exception will be thrown
-                    new CultureInfo(x);
-                    return true;
+
+                    var culture = new CultureInfo(x);
+                    return culture != null;
                 }
                 catch
                 {

src/Web/Grand.Web.Admin/Validators/Localization/LanguageValidator.cs

@@ -21,8 +21,8 @@ public LanguageValidator(
                 try
                 {
                     //create a CultureInfo object
-                    new CultureInfo(x);
-                    return true;
+                    var culture = new CultureInfo(x);
+                    return culture != null;
                 }
                 catch
                 {