Fix #1820: condition of whether generates outer

Previously, we don't generate `outer` for the anonymous class `new Inner2 {}`.
This is incorrect, as `Inner2 {}` extends `A.Inner`, which requires an outer.

trait A {
  val a = "a"
  trait Inner {
    def f = println(a)
    def h = 3
  }
}

trait B extends A {
  trait Inner2 extends Inner
  new Inner2 {}
}

1 files changed, 1 insertions, 0 deletions

diff --git a/tests/run/i1820b.check b/tests/run/i1820b.check
new file mode 100644
index 000000000..789819226
--- /dev/null
+++ b/tests/run/i1820b.check
@@ -0,0 +1 @@
+a