add protection if part of the data is missing, so can do gdat('te_rho' with...

add protection if part of the data is missing, so can do gdat('te_rho' with only iter=1, rt-like, liuqe results without psitbx calculations for tcv

git-svn-id: https://spcsvn.epfl.ch/repos/TCV/gdat/trunk@8484 d63d8f72-b253-0410-a779-e742ad2e26cf