This code was recently adjusted by c456e3911, but that commit didn't get
the logic correct when finding the attnum to start walking the tuple in.
If there is a NULL, we need to start walking the tuple before it.
Author: David Rowley <dgrowleyml@gmail.com>
Reported-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/CAHewXNnb-s_=VdVUZ9h7dPA0u3hxV8x2aU3obZytnqQZ_MiROA@mail.gmail.com