Add empty zone notice

* Display a notice when a map doesn't have a zone with a suggestion to assign one.
* Avoiding a default zone as many maps are added from updates and may not get their proper zones until the requisite data is found.

src/map/map.cpp

@@ -532,6 +532,12 @@ void MapZoneDatabase::loadingFinished() {
 			}
 		}
 	}
+
+	// Check for maps with no zones
+	for (int i = 0; i < map_num; i++) {
+		if (map[i].zone == nullptr)
+			ShowNotice("MapZoneDatabase::loadingFinished: Map %s has no zone. Assigning a zone is highly encouraged.\n", map[i].name);
+	}
 }
 
 MapZoneDatabase map_zone_db;