Mark of Dishonor & Max Vigor Bug fix

Players have been using Mark of Dishonor cast on positive karma players
to set their max vigor to 100 without having second wind. This fixes
Mark of Dishonor (which sent an undefined value for VigorThresholdChange
if the target is positive karma) and it also bounds max vigor based on
80 + second wind skill / 5 so no future bugs will ever break max vigor.