top: Make locale issues non-fatal.

If the setlocale() call fails, emit a warning and sleep briefly so the
user has a chance to see the warning before we redraw the screen. Note
that we have no way of knowing exactly what is wrong, but at least we
can suggest that they check their environment.

MFC after: 1 week
Sponsored by: Klara, Inc.
Reviewed by: kevans
Differential Revision: https://reviews.freebsd.org/D49230