Clear buffer on write

Author: sakno

src/DotNext.IO/IO/PoolingBufferedStream.cs

@@ -222,7 +222,7 @@ public ValueTask WriteAsync(CancellationToken token = default)
         }
         else if (stream.CanWrite)
         {
-            task = WriteCoreAsync(out _, token);
+            task = WriteCoreAsync(token);
         }
         else
         {
@@ -232,6 +232,13 @@ public ValueTask WriteAsync(CancellationToken token = default)
         return task;
     }
 
+    private async ValueTask WriteCoreAsync(CancellationToken token)
+    {
+        await WriteCoreAsync(out var isWritten, token).ConfigureAwait(false);
+        if (isWritten)
+            Reset();
+    }
+
     private bool WriteCore()
     {
         Debug.Assert(stream is not null);