In case rank drops below -1

src/engine/gameManager/BuildingManager.java

@@ -798,7 +798,7 @@ public enum BuildingManager {
         // Attempt to write to database or delete the building
         // if we are destroying it.
 
-        if (rank == -1)
+        if (rank <= -1)
             success = DbManager.BuildingQueries.DELETE_FROM_DATABASE(building);
         else
             success = DbManager.BuildingQueries.updateBuildingRank(building, rank);