Fixes a bug in calculation of the alpha-disk ionization gradient for the relxilllpCp model, i.e., when setting switch_iongrad_type=2. Due to the bug, the logxi parameter may have been overestimated in some cases. More specifically, the quoted value was given closer to Rin of the accretion disk instead of at its maximal value at a radius of (11/9)^2*Rin as intended. A simple re-fit with this version and only logxi free will result in the correct value.