Ignore curses.curs_set errors

[xgi]

curs_set can error if the visibility value is not supported -- particularly, some terminals may not support an invisible cursor. This PR ignores such errors (since it is not a crucial feature) instead of crashing the client.

See:

• https://linux.die.net/man/3/curs_set
• https://pubs.opengroup.org/onlinepubs/7908799/xcurses/curs_set.html