fixed problem in OObjectEnumLazyList with contains and indexOf

OObjectEnumLazyList.class

Fixed problem in contains and indexOf of OObjectEnumLazyList which leads
to incorrect results.

The used list for contains and indexOf can have null-values which leads to incorrect results. Changed to the serializedList which contains the string values from database. 

Issue: https://github.com/orientechnologies/orientdb/issues/2685