bpo-37417: Fix error handling in bytearray.extend.

[brandtbucher]

bytearray.extend doesn't properly handle errors that arise during iteration of the argument:

Python 3.9.0a0 (heads/master:5150d32, Jun 26 2019, 10:55:32) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> array = bytearray()
>>> bad_iter = map(int, "X")
>>> array.extend(bad_iter)
ValueError: invalid literal for int() with base 10: 'X'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: <method 'extend' of 'bytearray' objects> returned a result with an error set

As far as I can tell, this bug is present on all versions of Python 3. This patch adds a fix and a regression test.

https://bugs.python.org/issue37417

[miss-islington]

Thanks @brandtbucher for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.7, 3.8.
🐍🍒⛏🤖

[miss-islington]

I'm having trouble backporting to 3.8. Reason: 'Error 110 while writing to socket. Connection timed out.'. Please retry by removing and re-adding the needs backport to 3.8 label.

[bedevere-bot]

GH-14408 is a backport of this pull request to the 3.7 branch.

[brandtbucher]

Thanks @serhiy-storchaka!

Just a heads-up, it looks like the 3.8 backport timed out...

[miss-islington]

Thanks @brandtbucher for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.8.
🐍🍒⛏🤖

[bedevere-bot]

GH-14410 is a backport of this pull request to the 3.8 branch.

[serhiy-storchaka]

Thank you for your contribution, @brandtbucher!