readline memory corruption when sys.stdin fd >= FD_SETSIZE for select()

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-03-02.19:48:15.854>
labels = ['extension-modules', '3.7', 'type-crash']
title = 'readline memory corruption when sys.stdin fd >= FD_SETSIZE for select()'
updated_at = <Date 2017-04-30.12:14:38.475>
user = 'https://github.com/gpshead'

bugs.python.org fields:

activity = <Date 2017-04-30.12:14:38.475>
actor = 'marienz'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2017-03-02.19:48:15.854>
creator = 'gregory.p.smith'
dependencies = []
files = ['46689']
hgrepos = []
issue_num = 29700
keywords = []
message_count = 9.0
messages = ['288825', '288826', '288829', '288831', '288832', '289098', '289133', '289836', '292627']
nosy_count = 5.0
nosy_names = ['gregory.p.smith', 'marienz', 'christian.heimes', 'martin.panter', 'xiang.zhang']
pr_nums = ['540']
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue29700'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6', 'Python 3.7']