Fix #4752: validate the username and email.

Oqtane.Shared/Models/UserValidateResult.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Oqtane.Models
+{
+    public class UserValidateResult
+    {
+        public bool Succeeded {  get; set; }
+
+        public IDictionary<string, string> Errors { get; set; } = new Dictionary<string, string>();
+    }
+}