Handle WebSocketClosedError and fix indentation error

[rectalogic]

Using sockjs-tornado==1.0.7 with tornado==6.2, we see millions of exceptions of the form:

  File "/site/venv/lib/python3.10/site-packages/sockjs/tornado/periodic.py", line 69, in _run
    next_call = self.callback()
  File "/site/venv/lib/python3.10/site-packages/sockjs/tornado/session.py", line 405, in _heartbeat
    self.handler.send_pack(proto.HEARTBEAT)
  File "/site/venv/lib/python3.10/site-packages/sockjs/tornado/transports/websocket.py", line 89, in send_pack
    self.write_message(message, binary)
  File "/site/venv/lib/python3.10/site-packages/tornado/websocket.py", line 336, in write_message
    raise WebSocketClosedError()

sockjs-tornado handles IOError but tornado is raising WebSocketClosedError. This PR handles both errors.

While fixing this, I also encountered and fixed this exception due to an incorrect indentation in sockjs/tornado/transports/htmlfile.py:

Traceback (most recent call last):
  File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/cureatr/dev/cureatr/server/notification/web/notification_server.py", line 11, in <module>
    from sockjs.tornado import SockJSRouter
  File "/tmp/sockjs-tornado/sockjs/tornado/__init__.py", line 3, in <module>
    from .router import SockJSRouter
  File "/tmp/sockjs-tornado/sockjs/tornado/router.py", line 11, in <module>
    from sockjs.tornado import transports, session, sessioncontainer, static, stats, proto
  File "/tmp/sockjs-tornado/sockjs/tornado/transports/__init__.py", line 10, in <module>
    from .htmlfile import HtmlFileTransport
  File "/tmp/sockjs-tornado/sockjs/tornado/transports/htmlfile.py", line 69
    self.set_status(500)
                        ^
IndentationError: unindent does not match any outer indentation level

[anvouk]

Hi @mrjoes, what do we need to do to make this pr merged and a new version tagged on pypi? the missing on_close call is quite the pain in the butt, and i'd prefer not to fork the entire repo over a single line of code... Thanks.