tests/stress/recursive_gen: Add test for recursive gen with iter.

tests/stress/recursive_gen.py

@@ -1,9 +1,18 @@
 # test deeply recursive generators
 
+# simple "yield from" recursion
 def gen():
     yield from gen()
-
 try:
     list(gen())
 except RuntimeError:
     print('RuntimeError')
+
+# recursion via an iterator over a generator
+def gen2():
+    for x in gen2():
+        yield x
+try:
+    next(gen2())
+except RuntimeError:
+    print('RuntimeError')