HTTP request handler: check sys.stderr != None before logging

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-08-11.23:56:49.134>
labels = ['type-bug', 'library', '3.9']
title = 'HTTP request handler: check sys.stderr != None before logging'
updated_at = <Date 2021-08-13.23:02:22.093>
user = 'https://bugs.python.org/xiaolingbao'

bugs.python.org fields:

activity = <Date 2021-08-13.23:02:22.093>
actor = 'terry.reedy'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-08-11.23:56:49.134>
creator = 'xiaolingbao'
dependencies = []
files = []
hgrepos = []
issue_num = 44894
keywords = []
message_count = 2.0
messages = ['399423', '399470']
nosy_count = 1.0
nosy_names = ['xiaolingbao']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44894'
versions = ['Python 3.9']