(svn r22757) -Fix [FS#4730]: [NewGRF] Invalid memory access when querying the grfID of the default objects

src/newgrf_object.cpp

@@ -140,6 +140,11 @@ static uint32 GetObjectIDAtOffset(TileIndex tile, uint32 cur_grfid)
 
 	const ObjectSpec *spec = ObjectSpec::GetByTile(tile);
 
+	/* Default objects have no associated NewGRF file */
+	if (spec->grf_prop.grffile == NULL) {
+		return 0xFFFE; // Defined in another grf file
+	}
+
 	if (spec->grf_prop.grffile->grfid == cur_grfid) { // same object, same grf ?
 		return spec->grf_prop.local_id;
 	}