Fixed units pathfinding to nonexistent cores

core/src/io/anuke/mindustry/game/EventType.java

@@ -76,6 +76,7 @@ public class EventType{
         }
     }
 
+    /**Called when block building begins. The tile's block will nearly always be a BuildBlock.*/
     public static class BlockBuildEvent implements Event{
         public final Tile tile;
         public final Team team;