Read OUTCAR where # species in POSCAR/POTCAR differ

It is possible to run a VASP calculation where there are more species in the POTCAR file than POSCAR file. ase/io/vasp/read_vasp_out will fail to process an OUTCAR file when this is the case. This commit changes the file to only attempt to read the minium number of species between what is reported in the POTCAR file or the POSCAR.

This modification should only effect execution when there are more 'POTCAR:' lines in the file than species present in the 'ions per type' line (which I believe is read in from the POSCAR file). Otherwise, this program should run as before.