Asymmetric condition can cause map.users_pvp to be off in conjunction with OPTION_INVISIBLE

Originally posted by [b]Wildcard[/b]
I chanced upon this when researching [url="http://rathena.org/board/tracker/issue-1640-mob-spawns-disappearing/"]the issue of map.users being off[/url]. While it turned out to be unrelated, it presents a separate issue.

[u][b]How to reproduce[/b][/u]

1) Use @hide on a map with pvp disabled
2) Turn on pvp
3) Without unhiding, leave the map
4) Return to the map on another character (not @hidden). The pvp counter will display 2 combatants while there is really only one player on the map.

[u][b]Reconstruction[/b][/u]

@hide only modifies users_pvp if pvp is actually turned on. Since neither unit_remove_map nor clif_parse_LoadEndAck make such a distinction, it is possible to manipulate the value arbitrarily, leaving the map with "ghost" players for the pvp counter.

[u][b]Proposed Solution[/b][/u]

There are two possible approaches to this. The straightforward one is making the condition symmetric, and thus removing the check against the pvp flag in atcommand_hide, as shown here:
[attachment=893:athide.patch]

An alternative approach would remove the map variable users_pvp entirely, and iterate over all players on the map in question on demand, not counting those with OPTION_INVISIBLE. I assume the variable only exists for performance reasons in the first place, but suspect that with recent hardware developments, could easily be replaced.