Fix SingleConsumerUnboundedChannel WaitToReadAsync returning exception instead of false

src/libraries/System.Threading.Channels/src/System/Threading/Channels/SingleConsumerUnboundedChannel.cs

@@ -254,8 +254,7 @@ public override bool TryComplete(Exception? error)
                 // Complete a blocked reader if necessary
                 if (blockedReader is not null)
                 {
-                    error = ChannelUtilities.CreateInvalidCompletionException(error);
-                    blockedReader.TrySetException(error);
+                    blockedReader.TrySetException(ChannelUtilities.CreateInvalidCompletionException(error));
                 }
 
                 // Complete a waiting reader if necessary.  (We really shouldn't have both a blockedReader

src/libraries/System.Threading.Channels/tests/UnboundedChannelTests.cs

@@ -242,6 +242,23 @@ public async Task MultipleReaders_CancelsPreviousReader()
             Assert.Equal(42, await t2);
         }
 
+        [Fact]
+        public async Task WaitToReadAsync_ReturnsFalse_WhenReadAsyncWasCanceledAndChannelCompleted()
+        {
+            Channel<int> c = CreateChannel();
+
+            using var cts = new CancellationTokenSource();
+            ValueTask<int> readTask = c.Reader.ReadAsync(cts.Token);
+            cts.Cancel();
+            await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await readTask);
+
+            ValueTask<bool> waitTask = c.Reader.WaitToReadAsync(CancellationToken.None);
+
+            c.Writer.Complete();
+
+            Assert.False(await waitTask);
+        }
+
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsMultithreadingSupported))]
         public void Stress_TryWrite_TryRead()
         {