Compiler crash on call by name parameters used in inner classes.

[nicolasstucki]

class Fill(elem: => Int) {
  class Iter {
    def next(): Int = elem
  }
}

fails with

*** error while checking /Users/nicolasstucki/GitHub/dotty/compiler/../tests/run-wip/blabla.scala after phase arrayConstructors ***
java.lang.AssertionError: assertion failed: found:    (() => Int)(Fill.this.elem)
required: Int


tree = Fill.this.elem
	at scala.Predef$.assert(Predef.scala:165)
	at dotty.tools.dotc.transform.TreeChecker$Checker.adapt(TreeChecker.scala:459)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1596)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1594)
	at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:136)
	at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:57)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1594)
	at dotty.tools.dotc.transform.TreeChecker$Checker.typed(TreeChecker.scala:254)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1650)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedDefDef$1.apply(Typer.scala:1245)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedDefDef$1.apply(Typer.scala:1227)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:1227)
	at dotty.tools.dotc.transform.TreeChecker$Checker.dotty$tools$dotc$transform$TreeChecker$Checker$$super$typedDefDef(TreeChecker.scala:415)
...

This code is a minimization of an issue found while trying to compile the collection strawman with dotty (original code).