FLT_TEST 3D with MPI, out of bounds access in isobaric correction

[m.hadfield]

When running FLT_TEST with SOLVE3D defined, with MPI and bounds-checking enabled, an out of bounds error is triggered in step_floats_tile in the code that keeps the floats at their initial depth. The specific statement where the out-of-bounds error occurs is at line 292 in step_floats.F and the failure occurs for float l=231 (i.e. near the top of the grid). The reason it occurs is the horizontal locations, track(ixgrd,nfp1,l) and track(ixgrd,nfp1,l), appear not to have been initialised.

I will look into this further when I can.