[iter] Add tests for casting to hb_iter_t<> base class for hb_sorted_array_t<>

Something's phishy about hb_sorted_array_t<>.  Can't get it work nicely with
change I'm making.  Ugh..

src/test-iter.cc

diff --git a/src/test-iter.cc b/src/test-iter.cc
index 9ce8b0c..3de3401 100644
--- a/src/test-iter.cc
+++ b/src/test-iter.cc
@@ -91,7 +91,7 @@
 }
 
 template <typename Iterable,
-	 hb_enable_if (hb_is_iterable (Iterable))>
+	  hb_enable_if (hb_is_iterable (Iterable))>
 static void
 test_iterable (const Iterable &lst = Null(Iterable))
 {
@@ -127,6 +127,11 @@
   hb_set_t st;
   test_iterable (st);
   hb_sorted_array_t<int> sa;
+  (void) static_cast<hb_iter_t<hb_sorted_array_t<int>, hb_sorted_array_t<int>::item_t>&> (sa);
+  (void) static_cast<hb_iter_t<hb_sorted_array_t<int>, hb_sorted_array_t<int>::__item_t__>&> (sa);
+  (void) static_cast<hb_iter_t<hb_sorted_array_t<int>, int&>&>(sa);
+  (void) static_cast<hb_iter_t<hb_sorted_array_t<int>>&>(sa);
+  (void) static_cast<hb_iter_t<hb_array_t<int>, int&>&> (sa);
   test_iterable (sa);
 
   test_iterable<hb_array_t<int> > ();