Simplify scope split loops: remove unnecessary empty-entry checks

Agent-Logs-Url: https://github.com/modelcontextprotocol/csharp-sdk/sessions/bb2f14d3-4d60-438a-a84a-6f3b5c36cb8c

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

src/ModelContextProtocol.Core/Authentication/ClientOAuthProvider.cs

@@ -737,20 +737,17 @@ private async Task PerformDynamicClientRegistrationAsync(
         if (_lastRequestedScopes is not null && newScopes is not null)
         {
             var combined = new HashSet<string>(StringComparer.Ordinal);
+
             foreach (var scope in _lastRequestedScopes.Split(' '))
             {
-                if (scope.Length > 0)
-                {
-                    combined.Add(scope);
-                }
+                combined.Add(scope);
             }
+
             foreach (var scope in newScopes.Split(' '))
             {
-                if (scope.Length > 0)
-                {
-                    combined.Add(scope);
-                }
+                combined.Add(scope);
             }
+
             newScopes = string.Join(" ", combined);
         }