read_ic.c : change

change
StP[offset + n - header.npart[0]].Metal[k] = *fp++;
to
StP[n].Metal[k] = *fp++;

It improves the previous comment, when Ntask > 1,
however, in case of a lot of particles when a block
need to be splitted, this will fail !!!!

NEED TO IMPROVE

git-svn-id: https://svn.epfl.ch/svn/gasp@38 67b3a02f-582b-4e65-a7f6-2b87bd0cff7a