Fix nil mod type check Condition Weaponset

mod type condition can have varList instead of var, this pr validate
if we have var and the check if this condition if about weaponSet
closes PathOfBuildingCommunity/PathOfBuilding-PoE2#317

Author: justjuangui

src/Modules/CalcSetup.lua

@@ -157,7 +157,7 @@ function calcs.buildModListForNode(env, node, incSmallPassiveSkill)
 			local added = false
 			for j, extra in ipairs(mod) do
 				-- if type conditional and start with WeaponSet then update the var to the current weapon set
-				if extra.type == "Condition" and extra.var:match("^WeaponSet") then
+				if extra.type == "Condition" and extra.var and extra.var:match("^WeaponSet") then
 					mod[j].var = "WeaponSet".. node.allocMode
 					added = true
 					break