GROOVY-5865: DefaultGroovyMethods.getAt(List, Range) delegates now to getAt(List, EmptyRange) in case of EmptyRange.

This fixes issue with inconsistent behavior of getAt(List, Collection) where element of collection is EmptyRange. For details please see the JIRA ticket.
Merge pull request #107 from michal-mally/GROOVY-5865

GROOVY-5865: DefaultGroovyMethods.getAt(List, Range) delegates now to getAt(List, EmptyRange) in case of EmptyRange (applying but might tweak your solution)