pgsql: Downgrade error in object_aclmask_ext() to internal

Downgrade error in object_aclmask_ext() to internal

The "does not exist" error in object_aclmask_ext() was written as
ereport(), suggesting that it is user-facing. This is problematic:
get_object_class_descr() is meant to be for internal errors only and
does not support translation.

For the has_xxx_privilege functions, the error has not been
user-facing since commit 403ac226ddd. The remaining users are
pg_database_size() and pg_tablespace_size(). The call stack here is
pretty deep and this dependency is not obvious. Here we can put in an
explicit existence check with a bespoke error message early in the
function.

Then we can downgrade the error in object_aclmask_ext() to a normal
"cache lookup failed" internal error.

Reviewed-by: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Discussion: https://www.postgresql.org/message-id/flat/da2f8942-be6d-48d0-ac1c-a053370a6b1f(at)eisentraut(dot)org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b6463ea6ef3e46b32be96a23f3a9f47357847ce4

Modified Files
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src/backend/catalog/aclchk.c | 10 ++--------
src/backend/utils/adt/dbsize.c | 18 ++++++++++++++++++
2 files changed, 20 insertions(+), 8 deletions(-)