fixes 2 gameticker.dm bugs

fixes two bugs in gameticker.dm :
1.) the default value for hide_mode MUST be 0, otherwise all modes even outside Secret rounds will show up as a Secret round with no possible modes. the proper way of hiding the actual mode in Secret is letting /datum/controller/gameticker/proc/setup() deal with it.
if you want to reproduce this, switch your server to any other mode before roundstart, it will still say Secret with no possible modes.

2.) if there are no /obj/effect/landmark/spacepod/random placed on the map, pick(L) triggered a runtime error because the list was emtpy. a simple len check takes care of that.