tests: Add testcase for yielding from a stopped generator.

tests/basics/gen_yield_from_stopped.py

+# Yielding from stopped generator is ok and results in None
+
+def gen():
+    return 1
+    # This yield is just to make this a generator
+    yield
+
+f = gen()
+
+def run():
+    print((yield from f))
+    print((yield from f))
+    print((yield from f))
+
+try:
+    next(run())
+except StopIteration:
+    print("StopIteration")