Try queries must not crash if the entity is not found

force to inherit from sequencer to improve readibility

Svelto.ECS/DataStructures/TypeSafeDictionary.cs

@@ -52,9 +52,7 @@ namespace Svelto.ECS.Internal
             {
                 for (var i = 0; i < count; i++)
                 {
-                    var entityView = buffer[i];
-
-                    Add(entityView.ID.entityID, entityView);
+                    Add(buffer[i].ID.entityID, ref buffer[i]);
                 }
             }
             catch (Exception e)
@@ -169,6 +167,11 @@ namespace Svelto.ECS.Internal
             return findIndex;
         }
         
+        public bool TryFindElementIndex(int entityGidEntityId, out uint index)
+        {
+            return FindIndex(entityGidEntityId, out index);
+        }
+        
         static readonly Type _type = typeof(TValue);
     }
 }

Svelto.ECS/EntitiesDB.cs

@@ -64,9 +64,7 @@ namespace Svelto.ECS.Internal
                 return null;
             }
 
-            if (casted != null)
-                index = casted.FindElementIndex(entityGID.entityID);
-            else
+            if (casted == null || casted.TryFindElementIndex(entityGID.entityID, out index) == false)
             {
                 index = 0;
                 return null;

Svelto.ECS/Extensions/Unity/GenericEntityDescriptorHolder.cs

@@ -1,14 +0,0 @@
-#if UNITY_5 || UNITY_5_3_OR_NEWER
-namespace Svelto.ECS
-{
-    public class GenericEntityDescriptorHolder<T>: 
-        UnityEngine.MonoBehaviour , IEntityDescriptorHolder
-            where T: IEntityDescriptor, new()
-    {
-        public IEntityBuilder[] GetEntitiesToBuild()
-        {
-            return EntityDescriptorTemplate<T>.descriptor.entitiesToBuild;
-        }
-    }
-}
-#endif

Svelto.ECS/Sequencer.cs

@@ -47,7 +47,7 @@ namespace Svelto.ECS
         void Next<T, C>(IEngine engine, ref T param, C condition) where C : struct, IConvertible;
     }
 
-    public class Sequencer : ISequencer
+    public abstract class Sequencer : ISequencer
     {
         public void SetSequence(Steps steps)       
         {