Fixing nearest-neighbour interpolation in parcels.h for new --index in search_linear_float
Fixing nearest-neighbour interpolation in parcels.h for new --index in search_linear_float

Since commit c760cbc, search_linear_float returns —index if it is the
last one (deepest, northern, or easternmost). Therefore, we don’t need
explicit check for last index in nearest-neighbour interpolation anymore

OceanPARCELS/parcels,OceanPARCELS/parcels