[Groff] Bug in \m

[Bob Diertens]

Hi,

In developing the next release of gpresent, I discovered a bug
in \m
Consider this

    black\m[blue]blue\m[red]red\m[]blue\m[]red

I expect blue to be in blue and red to be in red, but the last
blue and red are in black.
It seems that \m[] changes back to the default color instead of
the previous one.

Can someone fix this?

Greetings,
    Bob