[test] Additional coverage in test_set_iter.

This adds a couple extra entries to the set used, such that iteration
would fail in 1.6.2 due to the bug in hb_set_t::page_t::next().

test/api/test-set.c

diff --git a/test/api/test-set.c b/test/api/test-set.c
index de23c55..b3dc35e 100644
--- a/test/api/test-set.c
+++ b/test/api/test-set.c
@@ -201,6 +201,8 @@
   hb_set_add (s, 13);
   hb_set_add_range (s, 6, 6);
   hb_set_add_range (s, 10, 15);
+  hb_set_add (s, 1100);
+  hb_set_add (s, 1200);
   hb_set_add (s, 20005);
 
   test_not_empty (s);
@@ -218,6 +220,10 @@
   g_assert (hb_set_next (s, &next));
   g_assert_cmpint (next, ==, 15);
   g_assert (hb_set_next (s, &next));
+  g_assert_cmpint (next, ==, 1100);
+  g_assert (hb_set_next (s, &next));
+  g_assert_cmpint (next, ==, 1200);
+  g_assert (hb_set_next (s, &next));
   g_assert_cmpint (next, ==, 20005);
   g_assert (!hb_set_next (s, &next));
   g_assert_cmpint (next, ==, HB_SET_VALUE_INVALID);
@@ -230,6 +236,12 @@
   g_assert_cmpint (first, ==, 10);
   g_assert_cmpint (last,  ==, 15);
   g_assert (hb_set_next_range (s, &first, &last));
+  g_assert_cmpint (first, ==, 1100);
+  g_assert_cmpint (last,  ==, 1100);
+  g_assert (hb_set_next_range (s, &first, &last));
+  g_assert_cmpint (first, ==, 1200);
+  g_assert_cmpint (last,  ==, 1200);
+  g_assert (hb_set_next_range (s, &first, &last));
   g_assert_cmpint (first, ==, 20005);
   g_assert_cmpint (last,  ==, 20005);
   g_assert (!hb_set_next_range (s, &first, &last));