ARC: yet another silly bugfix

tests/destructor/tarc2.nim

@@ -0,0 +1,29 @@
+discard """
+  output: '''leak: true'''
+  cmd: '''nim c --gc:arc $file'''
+"""
+
+type
+  T = ref object
+    s: seq[T]
+    data: string
+
+proc create(): T = T(s: @[], data: "abc")
+
+proc addX(x: T; data: string) =
+  x.data = data
+
+proc addX(x: T; child: T) =
+  x.s.add child
+
+proc main(rootName: string) =
+  var root = create()
+  root.data = rootName
+  # this implies we do the refcounting wrong. We should leak memory here
+  # and not create a destruction cycle:
+  root.addX root
+
+let mem = getOccupiedMem()
+main("yeah")
+# since we created a retain cycle, we MUST leak memory here:
+echo "leak: ", getOccupiedMem() - mem > 0