Fix placing multiple units on the same tile (#2)

Reviewed-on: #2
Reviewed-by: Ader_Alisma <ader.alisma.1@ens.etsmtl.ca>

Assets/Scripts/Drag&Drop/ObjectPlaceholder.cs

@@ -3,34 +3,44 @@
 public class ObjectPlaceholder : UnitPlaceholder
 {
     public GameObject Prefab { get; set; }
+
     public override void Place()
     {
         base.Place();
         Prefab.Create(transform.position, parent : LevelManager.Instance.LevelTransform);
     }
+
     public override bool CanBePlacedHere()
     {
         var objsOnPosition = LevelManager.Instance.GetAll<ILevelObject>(obj => obj.Position.IsContainedIn(transform.position));
         var positionIsCollidable = objsOnPosition.Exists(obj => obj.IsCollidable);
 
+        // If an ally is on the tile, we can't place anything here
+        foreach (var item in objsOnPosition)
+        {
+            if (item is Ally) 
+            {
+                return false;
+            }
+        }
+
         var defaultUnitCost = GlobalConfig.Instance.Current.populationCostPerUnit;
         return !positionIsCollidable 
             && LevelBoundCache.Contains(transform.position)
             && ResourceManager.Instance.EnoughFor(Rock, Wood, Food)
             && (Prefab.GetComponent<Building>()
             || ResourceManager.Instance.EnoughPopulationFor(defaultUnitCost)) 
-            && IsFarmerAndAllowed();
+            && IsHarvesterAndAllowed();
     }
 
-    private bool IsFarmerAndAllowed()
+    private bool IsHarvesterAndAllowed()
     {
         Ally unit = Prefab.GetComponent<Ally>();
         
-        //Obtiens info correctement.
+        // Get info
         LevelTile pointedTile = LevelManager.Instance.Get<LevelTile>(obj => obj.Position.IsContainedIn(transform.position));
 
         return unit is not Harvester || (unit is Harvester && IsAllowedTile(pointedTile));
-        //return true;
     }
 
     private bool IsAllowedTile(LevelTile pointedTile)

Assets/Scripts/Drag&Drop/UnitPlaceholder.cs

@@ -16,5 +16,6 @@ public abstract class UnitPlaceholder : DraggablePlaceholder
         return base.CanBePlacedHere() && ResourceManager.Instance.EnoughFor(Rock, Wood, Food) 
             && !LevelManager.Instance.Has<ILevelObject>(obj => obj.Position.IsContainedIn(transform.position));
     }
+
     public event System.Action<UnitPlaceholder> WasPlaced;
 }

Assets/Scripts/LevelManager/LevelManagerScript.cs

@@ -59,6 +59,7 @@ public class LevelManagerScript : SingletonBehaviour<LevelManagerScript>
     {
         //only when the level is loaded do we start updating
         updateAction = LevelManager.Instance.UpdateLevel;
+        LevelManager.Instance.LevelTransform = transform;
     }
 
     /// <summary>