Merge pull request #18 from mackysoft/support-concrete-base-class

`SubclassSelector` is now support a concrete base class.

Author: mackysoft

Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SubclassSelectorDrawer.cs

@@ -64,7 +64,7 @@ TypePopupCache GetTypePopup (SerializedProperty property) {
 
 				Type baseType = ManagedReferenceUtility.GetType(managedReferenceFieldTypename);
 				var popup = new AdvancedTypePopup(
-					TypeCache.GetTypesDerivedFrom(baseType).Where(p =>
+					TypeCache.GetTypesDerivedFrom(baseType).Append(baseType).Where(p =>
 						(p.IsPublic || p.IsNestedPublic) &&
 						!p.IsAbstract &&
 						!p.IsGenericType &&