Array offsets in recursive structures do not include the accumulated
offset. This diff fixes the mistake and adds a test.
Fixesgolang/go#29318
Change-Id: Iaa2a2f9404e4ed0e38b87e5e041709c1a8e25809
Reviewed-on: https://go-review.googlesource.com/c/154665
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>