Core/Spells: More generic implementation of Combustion

Closes #60 & #78

src/server/game/Entities/Player/Player.cpp

@@ -19630,6 +19630,10 @@ void Player::RemoveSpellMods(Spell * spell)
 
 void Player::DropModCharge(SpellModifier * mod, Spell * spell)
 {
+    // this mod shouldn't be removed here
+    if (mod->op == SPELLMOD_CRIT_DAMAGE_BONUS)
+        return;
+
     if (spell && mod->ownerAura && mod->charges > 0)
     {
         --mod->charges;