Non-UDMP Reach Failure

[scrasmussen]

Describe the bug
When running non-UDMP reach configuration, as a user increase the number of MPI ranks, there will reach a point where a rank will have no routing cells and will fail. It will not fail gracefully but with a bad-memory related SEGFAULT. This means that while using debugging tools it will sometimes report the program failing in differing, non-deterministic locations.

To Reproduce
Steps to reproduce the behavior:

1. Set UDMP_OPT = 0 in hydro.namelist
2. Use a reach-based configuration for channel routing

Expected behavior
Program should run to completion without SEGFAULT with any number of MPI ranks.