fixes #12747 [backport] (#13651)

* fixes #12747
* fix tests
* improve code style

Co-authored-by: cooldome <ariabushenko@bk.ru>
(cherry picked from commit 613ea6e85e)

tests/iter/titer11.nim

@@ -26,3 +26,14 @@ var output = represent(s)
 
 for item in output():
   echo item
+
+
+#------------------------------------------------------------------------------
+# Issue #12747
+
+type
+  ABC = ref object
+      arr: array[0x40000, pointer]
+let a = ABC()
+for a in a.arr:
+    assert a == nil