#20 liquidWriteArchive bug with particles

[Andrew Chapman]

Currently, if you execute the liquidWriteArchive mel
command, specifying a particle object to write to a RIB
file, it will give the correct result if you do it
after doing a normal liquid render.

However, if you haven't yet done a render, then the RIB
file exported will have no particles in it.

I think it is something like the current time not being
passed through liquidWriteArchive to the particle
class, so you end up with the state of things at the
last time a full render was done, or defaulting to time
0, when there are no birthed particles... maybe