Fixed `sv_vote_gametype_options` so that it defaults to the current gametype if it has no valid gametypes.

sv_vote_gametype 0 should be used instead of sv_vote_gametype_options "" but there shouldn't be this many errors due to simple user mistake.

If sv_vote_gametype_options has no valid gametypes, default to current one, if it's somehow possible that the current gamemode isn't valid then that will default to Deathmatch.

This fixes many issues with invalid sv_vote_gametype_options strings give invalid gametype masks for gametype filtering when filtering maps based on mapinfo's gametypes.

For example even if sv_vote_gametype_options is set to " " players are able to call votes for nextmap <any map supported by the current gametype> or gotomap.