False positive on E1101 when combining str.join with += operator

[themiurge]

Steps to reproduce

1. Run pylint on the following code snippet:

from collections import namedtuple

SomeClass = namedtuple('SomeClass', ['name'])

items = [SomeClass(name='some name')]

some_str = 'Items:\n'
some_str += ', '.join(item.name for item in items)

Current behavior

The some_str += ... line gets flagged as:

E1101: Instance of 'str' has no 'name' member (no-member)

The following (i.e. removing the += operator) works fine:

...
some_str = some_str + ', '.join(item.name for item in items)

The following also works fine:

...
item_names = (item.name for item in items)
some_str = 'Items:\n'
some_str += ', '.join(item_names)

Expected behavior

No error.

pylint --version output

pylint 2.3.1
astroid 2.2.5
Python 3.5.2 (default, Nov 12 2018, 13:43:14) 
[GCC 5.4.0 20160609]