Implement ReadAsync in ZipAESStream, extra simple version

src/ICSharpCode.SharpZipLib/Encryption/ZipAESStream.cs

@@ -1,6 +1,8 @@
 using System;
 using System.IO;
 using System.Security.Cryptography;
+using System.Threading;
+using System.Threading.Tasks;
 using ICSharpCode.SharpZipLib.Core;
 using ICSharpCode.SharpZipLib.Zip;
 
@@ -91,6 +93,13 @@ public override int Read(byte[] buffer, int offset, int count)
 			return nBytes;
 		}
 
+		/// <inheritdoc/>
+		public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+		{
+			var readCount = Read(buffer, offset, count);
+			return Task.FromResult(readCount);
+		}
+
 		// Read data from the underlying stream and decrypt it
 		private int ReadAndTransform(byte[] buffer, int offset, int count)
 		{