pgsql: nbtree VACUUM: Cope with buggy opclasses.

nbtree VACUUM: Cope with buggy opclasses.

Teach nbtree VACUUM to press on with vacuuming in the event of a page
deletion attempt that fails to "re-find" a downlink for its child/target
page.

There is no good reason to treat this as an irrecoverable error.  But
there is a good reason not to: pressing on at this point removes any
question of VACUUM not making progress solely due to misbehavior from
user-defined operator class code.

Discussion: https://postgr.es/m/CAH2-Wzma5G9CTtMjbrXTwOym+U=aWg-R7=-htySuztgoJLvZXg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5b861baa550a369e04bf67fbe83f3a5a8c742fb4

Modified Files
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src/backend/access/nbtree/nbtpage.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)