test(tests/playground/badreset): add test that exposes a bad reset/reuse placement

The generated code is safe, but the `reset/reuse` optimization will
never be applicable at runtime. The issue is that
`insert_reset_reuse_fn` is not checking the joint points.
I will fix the bug only at `resetreuse.lean`.

tests/playground/badreset.lean

@@ -0,0 +1,12 @@
+@[noinline] def g (x : Nat × Nat) := x
+
+set_option trace.compiler.boxed true
+
+@[noinline] def f (b : Bool) (x : Nat × Nat) : (Nat × Nat) × (Nat × Nat) :=
+let done (y : Nat × Nat) := (g (g (g y)), x) in
+match b with
+| true  := match x with | (a, b) := done (a, 0)
+| false := match x with | (a, b) := done (0, b)
+
+def main (xs : List String) : IO Unit :=
+IO.println $ f true (xs.head.toNat, xs.tail.head.toNat)