Issue detected by nvidia (nvhpc) compiler with -O2 or greater

nvhpc compiler option uses the following flags for optimization mode now:

`FLAGS = -fast -O3 -Mdclchk`

For some reason, -O3 or -O2 flag cause index error at line `reachID(1:nRch) = reachID( ixRch_order )` in [mpi_process.f90](https://github.com/ESCOMP/mizuRoute/blob/f500ec3907830851e2eff7b2cfea8a0acfc198f2/route/build/src/mpi_process.f90#L247).

Looks like `ixRch_order` get zero values for some reason.

With this flag,

`FLAGS = -O1 -Mdclchk `

works fine. Also, `MODE=debug` works fine.

Will need to look into this more why ixRch_order gets zero values with higher optimization mode.