disable teleports to cities that are destroyed or errant

src/engine/objects/City.java

@@ -306,8 +306,22 @@ public class City extends AbstractWorldObject {
             if (city.parentZone == null)
                 continue;
 
-            //can't repledge to a guild you're already part of
+            // Can't teleport to something without a tree
+
+            if (city.getTOL() == null)
+                continue;
+
+            // No abandoned cities
+
+            if (city.getTOL().getGuild().isEmptyGuild())
+                continue;
+
+            // No destroyed cities
 
+            if (city.getTOL().getRank() == -1)
+                continue;
+
+            //can't repledge to a guild you're already part of
             if (repledge && city.getGuild().equals(playerCharacter.guild))
                 continue;