Corrected script command instance ID lookups

* Fixes #2448.
* Resolves script_instancegetid causing scripts to end prematurely during player lookups.
Thanks to @Yuchinin and @Atemo!

src/map/script.cpp

@@ -19718,7 +19718,7 @@ unsigned short script_instancegetid(struct script_state* st)
 		struct guild *gd = NULL;
 		struct clan *cd = NULL;
 
-		if (script_rid2sd(sd)) {
+		if ((sd = map_id2sd(st->rid))) {
 			if (sd->instance_id)
 				instance_id = sd->instance_id;
 			if (instance_id == 0 && sd->status.party_id && (pd = party_search(sd->status.party_id)) != NULL && pd->instance_id)