These may be null, make sure we don't throw

Author: shana

src/GitHub.Api/ApplicationManagerBase.cs

@@ -176,8 +176,8 @@ protected virtual void Dispose(bool disposing)
             {
                 if (disposed) return;
                 disposed = true;
-                CancellationTokenSource.Cancel();
-                repositoryManager.Dispose();
+                if (CancellationTokenSource != null) CancellationTokenSource.Cancel();
+                if (repositoryManager != null) repositoryManager.Dispose();
             }
         }