fix IsImmune function

pkg/data/npc.go

@@ -99,8 +99,9 @@ func (m Monsters) FindByID(id UnitID) (Monster, bool) {
 
 func (m Monster) IsImmune(resist stat.Resist) bool {
 	for st, value := range m.Stats {
-		// Only consider immunity threshold (>= 100).
-		if value < 100 {
+		// We only want max resistance
+		// Need to cast to int32 because type is uint32 and negative values are possible (e.g. -50 for Andariel)
+		if int32(value) < 100 {
 			continue
 		}
 		if resist == stat.ColdImmune && st == stat.ColdResist {