Reintialize page in allocNewBuffer only when buffer is returned (#12399)

## Problem

See https://github.com/neondatabase/neon/issues/12387

`allocNewBuffer` initialise page with zeros 
but not always return it because of parity checks.
In case of wrong parity the page is rejected and as a result we have
dirty page with zero LSN, which cause assertion failure on neon_write
when page is evicted from shared buffers.

## Summary of changes

Perform, page initialisation in `allocNewBuffer` only when buffer is
returned (parity check is passed).

Postgres PRs:
https://github.com/neondatabase/postgres/pull/661
https://github.com/neondatabase/postgres/pull/662
https://github.com/neondatabase/postgres/pull/663
https://github.com/neondatabase/postgres/pull/664

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
Co-authored-by: Kosntantin Knizhnik <konstantin.knizhnik@databricks.com>

vendor/revisions.json

@@ -1,18 +1,18 @@
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+    "aaaeff2550d5deba58847f112af9b98fa3a58b00"
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   "v14": [
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 }