tests/basics: Add test for throw into yield-from with normal return.

This test was found by missing coverage of a branch in py/nativeglue.c.

tests/basics/gen_yield_from_throw.py

@@ -34,3 +34,17 @@ try:
     print(next(g))
 except TypeError:
     print("got TypeError from downstream!")
+
+# thrown value is caught and then generator returns normally
+def gen():
+    try:
+        yield 123
+    except ValueError:
+        print('ValueError')
+    # return normally after catching thrown exception
+def gen2():
+    yield from gen()
+    yield 789
+g = gen2()
+print(next(g))
+print(g.throw(ValueError))