Mod_DecompressVis_set (via Mod_LeafPVS_set) can be used to recycle pvs
sets, but the set may have been set to everything at some stage, which
is implemented by inverting the set (making the set infinite) and having
1-bits remove elements from the set. This is most definitely not wanted
for pvs :)
Currently undecided what to do about Mod_DecompressVis_mix, thus the
fixme.
Fixes the flickering lights in any map where the camera is out of the
map for a single frame (eg, start.bsp, The Catacombs (hipnotic, hip2m3)).
9e2c474d38