Fix #6682: Add regression test

Author: nicolasstucki

tests/pos/i6682a.scala

@@ -0,0 +1,4 @@
+object O{
+  val v = [T] => (y:T) => (x:y.type) => 3
+  def m = v(v)
+}

tests/pos/i6682b.scala

@@ -0,0 +1,5 @@
+object O{
+  val v = [T] => (y:T) => (x:y.type) => 3
+  val u = [T] => (y:T) => (x:y.type) => 3
+  def m = v(u)
+}