Fix IAsyncEnumerable SkipLast for count = 0

Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/SkipLast.cs

@@ -1,6 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT License.
-// See the LICENSE file in the project root for more information. 
+// See the LICENSE file in the project root for more information.
 
 using System;
 using System.Collections.Generic;
@@ -64,12 +64,14 @@ public async Task SkipLast_Zero()
         }
 
         [Fact]
-        public void SkipLast_Zero_NoAlias()
+        public async Task SkipLast_Zero_NoAlias()
         {
             var xs = Xs();
             var ys = xs.SkipLast(0);
 
             Assert.NotSame(xs, ys);
+            var e = ys.GetAsyncEnumerator();
+            await HasNextAsync(e, 1);
         }
 
         private async IAsyncEnumerable<int> Xs()

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/SkipLast.cs

@@ -1,6 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT License.
-// See the LICENSE file in the project root for more information. 
+// See the LICENSE file in the project root for more information.
 
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -38,12 +38,13 @@ public static IAsyncEnumerable<TSource> SkipLast<TSource>(this IAsyncEnumerable<
                     return source;
                 }
 
-                count = 0;
+                return source.Wrap();
             }
 
             return Core(source, count);
 
-            static async IAsyncEnumerable<TSource> Core(IAsyncEnumerable<TSource> source, int count, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
+            static async IAsyncEnumerable<TSource> Core(IAsyncEnumerable<TSource> source, int count,
+                [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
             {
                 var queue = new Queue<TSource>();
 
@@ -57,8 +58,8 @@ static async IAsyncEnumerable<TSource> Core(IAsyncEnumerable<TSource> source, in
                         {
                             yield return queue.Dequeue();
                             queue.Enqueue(e.Current);
-                        }
-                        while (await e.MoveNextAsync());
+                        } while (await e.MoveNextAsync());
+
                         break;
                     }
                     else

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Wrap.cs

@@ -0,0 +1,14 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace System.Linq
+{
+    public static partial class AsyncEnumerable
+    {
+        internal static async IAsyncEnumerable<TSource> Wrap<TSource>(this IAsyncEnumerable<TSource> source)
+        {
+            await foreach (var e in source.ConfigureAwait(false))
+                yield return e;
+        }
+    }
+}