Doomsday Engine

Optimize|Client|Shadow Bias|BiasIllum: Allocate memory for bias interpolation when necessary

Bias light sources do not animate and they aren't usually linked to
the sector light level. This means that allocating storage for the
data used whilst interpolating changes at BiasIllum level is usually
unnecessary and a waste of memory.

BiasIllum now only allocates this data dynamically as needed while
interpolating a change in lighting. When interpolation is completed
this storage is then released automatically. This reduces the amount
of memory needed by at least twelve bytes per bias illumination point
in the general case.