Avoids usage of uninitialized memory when inversion fails.
That uninitialized memory can cause object to become visible when
it is supposed not to or other artifacts like that.
Longer term solution would be to check every instance of invert_m#
function and to explicit fallback when needed (possibly, using
extra utility functions).
In some heavy rigs matrix inverse can be 10% of computation time. This
reduces it to 2% by using Eigen's optimized 4x4 matrix inverse and SSE
matrix multiplication.
