Fix collection cache lookup failure with enum keys

fix nhibernate#3643

Author: fredericDelaporte

src/NHibernate/Async/Type/TypeHelper.cs

@@ -125,6 +125,7 @@ internal static async Task InitializeCollectionsAsync(
 					continue;
 				}
 
+				value = await (pair.Value.KeyType.AssembleAsync(value, session, null, cancellationToken)).ConfigureAwait(false);
 				var collection = session.PersistenceContext.GetCollection(new CollectionKey(pair.Value, value));
 				await (collection.ForceInitializationAsync(cancellationToken)).ConfigureAwait(false);
 				assembleRow[pair.Key] = collection;

src/NHibernate/Type/TypeHelper.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using NHibernate.Collection;
@@ -133,6 +133,7 @@ internal static void InitializeCollections(
 					continue;
 				}
 
+				value = pair.Value.KeyType.Assemble(value, session, null);
 				var collection = session.PersistenceContext.GetCollection(new CollectionKey(pair.Value, value));
 				collection.ForceInitialization();
 				assembleRow[pair.Key] = collection;