Fix reporting of errors from ErrorTrees

Reporter#hasErrors only checks the current Reporter, we need to use
Reporter#errorsReported to take into account errors from outer Reporters.

Author: smarter

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2251,7 +2251,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
      *  tree that went unreported. A scenario where this happens is i1802.scala.
      */
     def ensureReported(tp: Type) = tp match {
-      case err: ErrorType if !ctx.reporter.hasErrors => ctx.error(err.msg, tree.pos)
+      case err: ErrorType if !ctx.reporter.errorsReported => ctx.error(err.msg, tree.pos)
       case _ =>
     }
 

tests/neg/ensureReported.scala

@@ -0,0 +1,6 @@
+object AnonymousF {
+  val f = {
+    case l @ List(1) => // error: missing parameter type // error: Ambiguous overload
+      Some(l)
+  }
+}