bzr-tiplog crashes on redirection

[Eli Zaretskii]

  D:\gnu\bzr\emacs\djgpp>bzr tiplog > tip.log
  bzr: ERROR: exceptions.TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'

  Traceback (most recent call last):
    File "bzrlib\commands.pyo", line 946, in exception_to_return_code
    File "bzrlib\commands.pyo", line 1150, in run_bzr
    File "bzrlib\commands.pyo", line 699, in run_argv_aliases
    File "bzrlib\commands.pyo", line 721, in run
    File "bzrlib\cleanup.pyo", line 135, in run_simple
    File "bzrlib\cleanup.pyo", line 165, in _do_with_cleanups
    File "bzrlib\commands.pyo", line 1165, in ignore_pipe
    File "D:/usr/Bazaar/plugins\tiplog\commands.py", line 83, in run
    File "D:/usr/Bazaar/plugins\tiplog\commands.py", line 51, in truncate
  TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'

  bzr 2.4.1 on python 2.6.6 (Windows-XP-5.1.2600-SP2)
  arguments: ['bzr', 'tiplog']
  plugins: automv[unknown], bisect[1.1.0dev], bzrtools[2.4.0],
      changelog_merge[2.4.1], colo[0.3.1dev], diffstat[0.2.0],
      difftacular[unknown], fastimport[0.12.0dev], git[0.6.2], grep[0.5.0dev],
      history_db[unknown], launchpad[2.4.1], loom[2.2.1dev],
      netrc_credential_store[2.4.1], news_merge[2.4.1], ping[unknown],
      pipeline[1.1.0], repodetails[1.9.0dev], rewrite[0.6.3dev],
      search[1.7.0dev], stats[0.1.0dev], svn[1.1.0], tiplog[0.0.1dev],
      upload[1.0.1dev], xmloutput[0.8.7]
  encoding: 'cp1255', fsenc: 'mbcs', lang: None

  *** Bazaar has encountered an internal error.  This probably indicates a
      bug in Bazaar.  You can help us fix it by filing a bug report at
	  https://bugs.launchpad.net/bzr/+filebug
      including this traceback and a description of the problem.

The same happens if I pipe tiplog's output to a pager, like Less.