message: Improve logging in the DownloadApplicationModeHandler.
  issue
diff: @@ -146,6 +146,7 @@ class DownloadSession {
  // Check for invalid characters which may indicate a crash on the remote side.
  if (invalidBodyRegex.test(this._encodedDataBuffer)) {
  + this._log.warn("Data buffer contains illegal characters. Aborting.");
  this._state = DownloadHandlerState.ERROR;
  this._closeFileHandle(false);
  return {action: TermApi.ApplicationModeResponseAction.ABORT, remainingData: this._encodedDataBuffer};
  