Calculating of Shield Block Value PCT modificators

[michalpolko]

Revision: 11 739

Custom patches: mangosR2/przemratajczak fork, problem exists on clean mangos

HOW IT WORKS NOW: Shield Block Value pct mods are multiplied by each other.

HOW IT SHOULD WORK: Shield Block Value pct mods should be additive always, all pct mods for this one particular "stat". A lot of research about this was done by many ppl, many proves etc.

Proposition of fix: https://github.com/mangosR2/mangos/commit/8c511f51b8bacee1da53a84adf111aa8266f9486#commitcomment-480692