Don't close asyncio subprocess stream if it's stdin is closed

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-05-05.18:30:29.393>
labels = ['type-bug', '3.8', 'expert-asyncio']
title = "Don't close subprocess stream if it's stdin is closed"
updated_at = <Date 2019-05-05.18:30:29.393>
user = 'https://github.com/asvetlov'

bugs.python.org fields:

activity = <Date 2019-05-05.18:30:29.393>
actor = 'asvetlov'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2019-05-05.18:30:29.393>
creator = 'asvetlov'
dependencies = []
files = []
hgrepos = []
issue_num = 36805
keywords = []
message_count = 1.0
messages = ['341467']
nosy_count = 2.0
nosy_names = ['asvetlov', 'yselivanov']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue36805'
versions = ['Python 3.8']