sched.py: run() is caught in delayfunc even if all events are cancelled.

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-06-06.12:06:26.419>
labels = ['type-feature', 'library', '3.9']
title = 'sched.py: run() is caught in delayfunc even if all events are cancelled.'
updated_at = <Date 2019-06-08.05:49:36.784>
user = 'https://github.com/ernestum'

bugs.python.org fields:

activity = <Date 2019-06-08.05:49:36.784>
actor = 'rhettinger'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-06-06.12:06:26.419>
creator = 'ernestum'
dependencies = []
files = []
hgrepos = []
issue_num = 37174
keywords = []
message_count = 3.0
messages = ['344804', '345021', '345023']
nosy_count = 4.0
nosy_names = ['tim.peters', 'rhettinger', 'terry.reedy', 'ernestum']
pr_nums = ['13862']
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue37174'
versions = ['Python 3.9']