Ignore inhibited particles in timestep

This should supersede !843 (closed).

The old test that crashed was mpirun -np 8 ../../swift_mpi --pin --cooling --star-formation --feedback --stars --cosmology --hydro --self-gravity -v 1 --threads=14 eagle_25.yml with the EAGLE subgrid model activated.

This now runs smoothly with the debugging checks activated.