Disruption Shield can never be negative

git-svn-id: http://svn.net-core.org/repos/t-engine4@2830 51575b47-30f0-44d4-a5cc-537603b46e54

game/modules/tome/data/talents/spells/arcane.lua

@@ -126,7 +126,7 @@ newTalent{
 	cooldown = 30,
 	sustain_mana = 150,
 	tactical = { DEFEND = 2 },
-	getManaRatio = function(self, t) return 3 - self:combatTalentSpellDamage(t, 10, 200) / 100 end,
+	getManaRatio = function(self, t) return 3 - math.max(self:combatTalentSpellDamage(t, 10, 200) / 100, 0.5) end,
 	activate = function(self, t)
 		local power = t.getManaRatio(self, t)
 		self.disruption_shield_absorb = 0