Fix sdf computation while `USE_SQUARED_DISTANCES`.

Function `map_fixed_to_sdf` expects spread to be absolute
and not squared.

* src/sdf/ftbsdf.c (finalize_sdf): Pass absolute spread
while `map_fixed_to_sdf`.

* src/sdf/ftsdf.c (sdf_generate_bounding_box): Ditto.
2 files changed