Filtertext on map and servername using ./bin/server status

(cherry picked from commit 49a39ba70772e42c9fa61d90c96f8d96c954f27a)
assert() the io.open() in server.write_server_status() to display a better error message

(cherry picked from commit 527583a4b9e82c0365710cdfc897a08b23dbc84f)