Follow up to e02e85b

Fixes #3721

Thanks to @teededung

src/map/battle.cpp

@@ -6847,7 +6847,7 @@ int64 battle_calc_return_damage(struct block_list* bl, struct block_list *src, i
 	sc = status_get_sc(bl);
 	ssc = status_get_sc(src);
 
-	if (sc->data[SC_WHITEIMPRISON])
+	if (sc && sc->data[SC_WHITEIMPRISON])
 		return 0; // White Imprison does not reflect any damage
 
 	if (flag & BF_SHORT) {//Bounces back part of the damage.