Describe the bug
:terminal isn't colored when termguicolors is on.

To Reproduce

$vim --clean
:set termguicolors
:terminal <a command that outputs some colored text>

Expected behavior

The text is colored.

Screenshots

• set termguicolors

• set notermguicolors

Environment:

Vim: 8.1.0884
OS: macOS Catalina 10.15
Terminal: Alacritty and mlterm

Additional context

This problem doesn't happen without this patch: e023e88