Relax the semantics of `Range.lastElement` for internal use.
Relax the semantics of `Range.lastElement` for internal use.

`lastElement` is only used in code paths where the range is
non-empty. It is therefore wasteful to try and give it a sort
of sensible value for empty ranges.

slothspot/scala,felixmulder/scala,slothspot/scala,lrytz/scala,slothspot/scala,lrytz/scala,shimib/scala,martijnhoekstra/scala,martijnhoekstra/scala,shimib/scala,martijnhoekstra/scala,slothspot/scala,lrytz/scala,scala/scala,jvican/scala,jvican/scala,shimib/scala,martijnhoekstra/scala,shimib/scala,jvican/scala,jvican/scala,martijnhoekstra/scala,scala/scala,jvican/scala,scala/scala,slothspot/scala,jvican/scala,felixmulder/scala,shimib/scala,felixmulder/scala,scala/scala,felixmulder/scala,lrytz/scala,felixmulder/scala,felixmulder/scala,scala/scala,slothspot/scala,shimib/scala,scala/scala,jvican/scala,lrytz/scala,lrytz/scala,felixmulder/scala,slothspot/scala,martijnhoekstra/scala