Subtitles: Add z-cord limit removed in 8f3d30412adad6bfa152c6ebf8738965bb79cf28.

Without limit we transform points not relalistic to render. Limit was
lowered from 1000 to 500. It is good enough and give bigger depth.

Add const to some values and remove definition of values used only once.
Rasterizer: Remove sanity checks.

They are imperfect and can cause valid "sane" subtitles to not
show. Instead check for memory allocation failures.
Properly catch bad allocation exception.