Avoid spurious error message

Avoid spurious error message
"cannot be tracked since its capture set is empty".

This arose in lazyref.scala for a DependentTypeTree in an anaonymois function.
Dependent type trees map to normal TypeTrees, not InferredTypeTrees (and things
go wrong if we try to change that).

Author: odersky

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

@@ -388,7 +388,7 @@ class CheckCaptures extends Recheck:
       def traverse(tree: Tree)(using Context) =
         tree match
           case _: InferredTypeTree =>
-          case tree: TypeTree =>
+          case tree: TypeTree if !tree.span.isZeroExtent =>
             knownType(tree).foreachPart(
               checkWellformedPost(_, tree.srcPos))
             knownType(tree).foreachPart {

tests/pos-custom-args/captures/lazyref.scala

@@ -0,0 +1,11 @@
+class CC
+type Cap = {*} CC
+
+class LazyRef[T](val elem: {*} () => T):
+  val get = elem
+
+def map[A, B](ref: {*} LazyRef[A], f: {*} A => B): {f, ref} LazyRef[B] =
+  new LazyRef(() => f(ref.elem()))
+
+def mapc[A, B]: (ref: {*} LazyRef[A], f: {*} A => B) => {f, ref} LazyRef[B] =
+  (ref1, f1) => map[A, B](ref1, f1)