Updated CHANGES.md file with issue description
@@ -71,5 +71,6 @@ Was originally in *HostConfigEntry*.
* [SSHD-1244](https://issues.apache.org/jira/browse/SSHD-1244) Re-defined channel identifiers as `long` rather than `int` to align with protocol UINT32 definition
* [SSHD-1246](https://issues.apache.org/jira/browse/SSHD-1246) Added SshKeyDumpMain utility
* [SSHD-1247](https://issues.apache.org/jira/browse/SSHD-1247) Added support for Argon2id encrypted PUTTY keys
+* [SSHD-1257](https://issues.apache.org/jira/browse/SSHD-1257) ChannelSession: don't flush out stream if already closed
