Fix fortify crash from party member config

Fixes #9318

Author: LocalIdentity

src/Modules/CalcPerform.lua

@@ -614,7 +614,8 @@ local function doActorMisc(env, actor)
 		end
 		-- Fortify
 		if modDB:Flag(nil, "Fortified") or modDB:Sum("BASE", nil, "Multiplier:Fortification") > 0 then
-			local skillModList = actor.mainSkill.skillModList
+			local skillModList = actor.mainSkill and actor.mainSkill.skillModList or actor.modDB
+			local skillCfg = actor.mainSkill and actor.mainSkill.skillCfg
 			local maxStacks = modDB:Override(nil, "MaximumFortification") or modDB:Sum("BASE", skillCfg, "MaximumFortification")
 			local minStacks = m_min(modDB:Flag(nil, "Condition:HaveMaxFortification") and maxStacks or modDB:Sum("BASE", nil, "MinimumFortification"), maxStacks)
 			local stacks = m_min(modDB:Override(nil, "FortificationStacks") or (alliedFortify > 0 and alliedFortify) or (minStacks > 0 and minStacks) or maxStacks, maxStacks)