pgsql: Fix thinko in nocachegetattr() and nocache_index_getattr()

Fix thinko in nocachegetattr() and nocache_index_getattr()

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

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7a2ab122a1c555ee4298863917ce68a2b9800cb8

Modified Files
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src/backend/access/common/heaptuple.c  | 9 +++++----
src/backend/access/common/indextuple.c | 9 +++++----
2 files changed, 10 insertions(+), 8 deletions(-)