SI-8951  SeqView and StreamView stack-overflow on negative index after flatMap
SI-8951  SeqView and StreamView stack-overflow on negative index after flatMap

Checks and throws IndexOutOfBounds now.

No test, caught and checked by scala-collections-laws (line 405 presently).

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