Update to list based lookup

src/engine/gameManager/BuildingManager.java

@@ -55,7 +55,7 @@ public enum BuildingManager {
 
         for (int i = 0; i < numOfSlots; i++) {
 
-            if (building.hirelings.get(i) != null)
+            if (building.hirelings.get(i) == null)
                 return i;
         }
         return -1;
@@ -75,7 +75,7 @@ public enum BuildingManager {
 
         for (int i = numOfSlots - 1; i >= 0; i--) {
 
-            if (!building.hirelings.contains(i))
+            if (building.hirelings.get(i) == null)
                 return i;
         }
         return -1;