tracked down a very fun bug... which i fixed in 2 out of 4 different ways so that it never ever happens again (story in description)

my level of detail code made initObjects take longer which made both
karts fall through the world which made them spawn in the same place
which in the new oncollide caused their differenc to be 0 which when
normalized resulted in NaN so one kart set their position to NaN which
meant the camera was set to NaN which meant the distance between
cameras and objects was NaN which made the LoD index NaN which i
luckily had an assert for otherwise i'd have been tracking it down for
even longer.

i fixed it both the easy way and the fun way
made GamePhysicalObject variables private