bug#38563: 27.0.50; Company popup renders with newlines (?) inheriting the bg properties of the character at next line's bol

[Dmitry Gutov]

Here's an unfortunate new behavior which I didn't have time to report
or properly describe before.

When the next line starts on a character that has a distinct background,
that background is inherited when displaying newlines inside the display
string that renders the popup.

Here are two ways I usually trigger it:

1. Initiate completion on the "Author:" line of a LogEdit buffer (the
next line is an inverse-video line).

2. Have at least one space at the beginning of a line, and have
whitespace-mode on to highlight it in red. Then initiate completion on
the preceding line.

Screenshots are attached.

Needless to say, the latest Emacs 26 doesn't exhibit this problem.

Screenshot from 2019-12-11 03-00-35.png
Description: PNG image

Screenshot from 2019-12-11 03-00-41.png
Description: PNG image