Code using structural type does not print error, crashes at Erasure

[helloqirun]

scalac compiles but dotc crashes.
In particular, scalac-2.11 gives one warning but 2.9 gives none.

$ cat abc.scala

object Test {
  def f(g: { val update: Unit }) = g.update
  def main(update: Array[String]) = {}
}

$ dotc abc.scala

exception while typing g.update of class class dotty.tools.dotc.ast.Trees$Select # 75
exception while typing def f(g: Object{update: Unit}): Unit = g.update of class class dotty.tools.dotc.ast.Trees$DefDef # 102
exception while typing @scala.annotation.internal.SourceFile("abc.scala") final module class Test$()
   extends
 Object() {
  def f(g: Object{update: Unit}): Unit = g.update
  def main(update: Array{scala$Array$$T = String}): Unit =
    {
      ()
    }
} of class class dotty.tools.dotc.ast.Trees$TypeDef # 115
exception while typing package <empty> {
  final lazy module val Test: Test$ = new Test$()
  @scala.annotation.internal.SourceFile("abc.scala") final module class Test$()
     extends
   Object() {
    def f(g: Object{update: Unit}): Unit = g.update
    def main(update: Array{scala$Array$$T = String}): Unit =
      {
        ()
      }
  }
} of class class dotty.tools.dotc.ast.Trees$PackageDef # 116

exception occurred while compiling abc.scala
Exception in thread "main" java.lang.AssertionError: NoDenotation.owner
	at dotty.tools.dotc.core.SymDenotations$NoDenotation.owner(SymDenotations.scala:1854)
	at dotty.tools.dotc.transform.Erasure$Typer.mapOwner$1(Erasure.scala:358)
	at dotty.tools.dotc.transform.Erasure$Typer.typedSelect(Erasure.scala:362)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1470)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1534)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:96)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1553)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1551)
	at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:136)
	at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:57)
<...>

[odersky]

Fixed by separate PR.