The water/gas pressures are only calculated if woc and goc lies within
the reservoar
The water/gas pressure is set to -inf when woc and goc is above or below
the reservoar.
Fixes issues pointed out in the PR comments
Merge pull request #630 from totto82/fix_init_spe9

The water/gas press. are calculated only if woc/goc is within the reservoar