add some is_user_connected checks to things
reset players m_flLastActivityTime to current game time when we go live

prevents players from instantly getting kicked when we turn on
mp_autokick, if they have been afk for longer than the value of
mp_autokick_timeout

for example, if a player .readys up after pregame voting has taken
place, then goes afk while waiting for everybody else to .ready or the
server to fill up, they will no longer instantly get kicked when the
game goes live if they've been afk longer than mp_autokick_timeout,
instead we reset their m_flLastActivityTime