[BUG] ISPH bug - particle in non-existent cell

[LonelyCat124]

Describe the bug
For the ISPH testcase, the domain is split into a 12x19 domain, however some particles are in cell {12,2} which can't exist.

Expected behavior
Particles should always be in a domain cell.

[LonelyCat124]

This happened because we treated a non-periodic example as periodic.
Keeping this open as something that needs to be dealt with for non-periodic cases.