pgsql: Avoid potential pfree on NULL on OpenSSL errors

Avoid potential pfree on NULL on OpenSSL errors

Guard against the pointer being NULL before pfreeing upon an error
returned from OpenSSL.  Also handle errors from X509_NAME_print_ex
which can return -1 on memory allocation errors.

Backpatch down to v15 where the code was added.

Author: Sergey Shinderuk <s.shinderuk@postgrespro.ru>
Discussion: https://postgr.es/m/8db5374d-32e0-6abb-d402-40762511eff2@postgrespro.ru
Backpatch-through: v15

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5f3aa309a880bb429c6a648d64e20fbd353fee8a

Modified Files
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src/backend/libpq/be-secure-openssl.c | 25 +++++++++++++++++--------
1 file changed, 17 insertions(+), 8 deletions(-)