Particles very near edge of domain can result in a seg fault due to rounding

If a coordinate is very close to outside the box, sometimes it can result in a seg fault.

Output from with debug checks for the offending particle

[00000.1] ../../.././src/space.c:space_parts_get_cell_index_mapper():2190: Invalid index=1728 cdim=[12 12 12] p->x=[3.7499999999999996e+00 2.600000e-01 0.000000e+00] a=[1.887104e-12 -4.481727e-08 0.000000e+00] v=[5.758984e-15 -1.367715e-10 0.000000e+00] old_v=[-3.552075e-13 -7.305726e-13 0.000000e+00] pid=3397 h=0.013000

The box size in this case is 3.75. Matthieu said essentially pos_x * s->iwidth[0] > s->dim[0], not sure if/how to work around but I can look into it tomorrow.