pgsql: Turn visibilitymap_clear() Assert back into an error

Turn visibilitymap_clear() Assert back into an error

Commit ed62d26caca fixed a bug in clearing the visibility map and, while
doing so, made some incidental changes to visibilitymap_clear(). One of
them replaced the error thrown when the wrong buffer is passed to
visibilitymap_clear() with an Assert().

While anyone adding a new visibilitymap_clear() caller should be running
assert-enabled builds, visibilitymap_set() still reports the same
wrong-buffer condition with an elog(ERROR), so visibilitymap_clear()
should also do so for consistency. This change was also unrelated to
the bug fix and is better made as a separate commit. Restore the error.

Reported-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAHGQGwF_PzOv5y7ucFh7Fqqqa8ar83zYwvWugqarRD6%2B7GCtEQ%40mail.gmail.com
Backpatch-through: 19

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4dbc54506c328a03070bf1a98309bdc05dac331d

Modified Files
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src/backend/access/heap/visibilitymap.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)