Fix error when HTTP version is missing in Python 3

[andrewisplinghoff]

I encountered the following error in the log of our web server running waitress 1.1.0 on Python 3.6.1:

uncaptured python exception, closing channel <waitress.channel.HTTPChannel connected 140.10.xxx.xxx:37060 at 0x17ed609aa90> (<class 'TypeError'>:decoding to str: need a bytes-like object, NoneType found [asyncore.py|read|83] [asyncore.py|handle_read_event|423] [lib\site-packages\waitress\channel.py|handle_read|174] [lib\site-packages\waitress\channel.py|received|191] [lib\site-packages\waitress\parser.py|received|102] [lib\site-packages\waitress\parser.py|parse_header|201] [lib\site-packages\waitress\compat.py|tostr|53])

The problem comes from the variable version being set to None if it is missing in the request and being transformed to a string afterwards.

waitress/waitress/parser.py

Line 296 in 77bb002

version = None

waitress/waitress/parser.py

Line 201 in 77bb002

version = tostr(version)

The suggested fix improves the Python 3 compatibility function to handle None values the same way as Python 2 does. Another fix would be of course to not try to convert None to a string in the first place.

[digitalresistor]

It should instead be changed to ignore the request entirely/return an error to the requesting client. If crack first line is unable to figure out the HTTP version used, then it is not something that Waitress can properly deal with in the first place.

See #110 for a similar issue.

Instead of converting it to None as a string, we should reject the request.

[digitalresistor]

I've just accepted and merged #252 instead of this patch, thanks for your contribution and apologies for sitting on it.