Added check to parse AuthResult from URI if post data is null.

src/client/Microsoft.Identity.Client/Platforms/Features/WinFormsLegacyWebUi/WindowsFormsWebAuthenticationDialogBase.cs

@@ -205,7 +205,7 @@ private bool CheckForClosingUrl(Uri url, byte[] postData = null)
                 url.AbsolutePath.Equals(_desiredCallbackUri.AbsolutePath))
             {
                 RequestContext.Logger.Info("[Legacy WebView] Redirect URI was reached. Stopping WebView navigation...");
-                Result = AuthorizationResult.FromPostData(postData);
+                Result = postData != null ? AuthorizationResult.FromPostData(postData) : AuthorizationResult.FromUri(url.OriginalString);
                 readyToClose = true;
             }