SI-6205 make pt fully defined before inferTypedPattern

refines my fix for SI-2038 (#981) by making pt fully defined before calling inferTypedPattern,
instead of making the result of inferTypedPattern fully defined

I finally realized my mistake by diffing the -Ytyper-debug output of compiling the variants with:

```
  x match {case Holder(k: A[kt]) => (k: A[kt])}
```

and

```
  (x: Any) match {case Holder(k: A[kt]) => (k: A[kt])}
```

1 files changed, 18 insertions, 0 deletions

diff --git a/test/files/pos/t6205.scala b/test/files/pos/t6205.scala
new file mode 100644
index 0000000000..02d924fe85
--- /dev/null
+++ b/test/files/pos/t6205.scala
@@ -0,0 +1,18 @@
+// original code by reporter
+class A[T]
+class Test1 {
+  def x(backing: Map[A[_], Any]) =
+    for( (k: A[kt], v) <- backing)
+      yield (k: A[kt])
+}
+
+// this tests same thing as above, but independent of library classes,
+// earlier expansions eliminated as well as variance (everything's invariant)
+case class Holder[A](a: A)
+class Mapped[A] { def map[T](f: Holder[A] => T): Iterable[T] = ??? }
+class Test2 {
+  def works(backing: Mapped[A[_]]): Iterable[A[_]]
+    = backing.map(x =>
+         x match {case Holder(k: A[kt]) => (k: A[kt])}
+      )
+}
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