Fix for System.Buffers.ArrayPool

LibZipSharp.UnitTest/ZipTests.cs

@@ -138,5 +138,24 @@ public void AddStreamDateCheck ()
 				Assert.AreEqual (date, WithoutMilliseconds (entry.ModificationTime), $"Check 1 {WithoutMilliseconds (entry.ModificationTime)} != {date}");
 			}
 		}
+
+		[Test]
+		public void SmallTextFile ()
+		{
+			var zipStream = new MemoryStream ();
+			var encoding = Encoding.UTF8;
+			using (var zip = ZipArchive.Create (zipStream)) {
+				zip.AddEntry ("foo", "bar", encoding);
+			}
+			using (var zip = ZipArchive.Open (zipStream)) {
+				var entry = zip.ReadEntry ("foo");
+				Assert.IsNotNull (entry, "Entry 'foo' should exist!");
+				using (var stream = new MemoryStream ()) {
+					entry.Extract (stream);
+					stream.Position = 0;
+					Assert.AreEqual ("bar", encoding.GetString (stream.ToArray ()));
+				}
+			}
+		}
 	}
 }

ZipArchive.cs

@@ -751,7 +751,7 @@ internal static unsafe Int64 stream_callback (IntPtr state, IntPtr data, UInt64
 					try {
 						Marshal.Copy (data, buffer, 0, length);
 						stream.Write (buffer, 0, length);
-						return buffer.Length;
+						return length;
 					} finally {
 						ArrayPool<byte>.Shared.Return (buffer);
 					}