Make dispose order consistent across the overloads

Ix.NET/Source/System.Interactive.Async/System/Linq/Operators/Amb.cs

@@ -202,10 +202,10 @@ namespace System.Linq
                         individualTokenSources[i].Cancel();
                     }
 
-                    await Task.WhenAll(cleanup).ConfigureAwait(false);
-
                     allIndividualDispose.Dispose();
 
+                    await Task.WhenAll(cleanup).ConfigureAwait(false);
+
                     throw;
                 }