Set default time of particles to grid.time[0]
Set default time of particles to grid.time[0]

Fixing an issue when pset.show() is called before particles are
advected. In that case, `time` was set to zero, even if the grid did
not have data for `time=0`. Now, the default value when particles are
initialised is `grid.time[0]`

OceanPARCELS/parcels,OceanPARCELS/parcels