Fix user agent missing in registration

osu.Game/Online/API/APIRequest.cs

@@ -162,16 +162,6 @@ namespace osu.Game.Online.API
             [JsonProperty("error")]
             public string ErrorMessage { get; set; }
         }
-
-        private class OsuWebRequest : WebRequest
-        {
-            public OsuWebRequest(string uri)
-                : base(uri)
-            {
-            }
-
-            protected override string UserAgent => "osu!";
-        }
     }
 
     public class APIException : InvalidOperationException

osu.Game/Online/API/OsuWebRequest.cs

@@ -0,0 +1,21 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.IO.Network;
+
+namespace osu.Game.Online.API
+{
+    public class OsuWebRequest : WebRequest
+    {
+        public OsuWebRequest(string uri)
+            : base(uri)
+        {
+        }
+
+        public OsuWebRequest()
+        {
+        }
+
+        protected override string UserAgent => "osu!";
+    }
+}

osu.Game/Online/API/RegistrationRequest.cs

@@ -2,11 +2,10 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using Newtonsoft.Json;
-using osu.Framework.IO.Network;
 
 namespace osu.Game.Online.API
 {
-    public class RegistrationRequest : WebRequest
+    public class RegistrationRequest : OsuWebRequest
     {
         internal string Username;
         internal string Email;