test/bio_base64_test.c: Add check for BIO_new()

test/bio_base64_test.c: Add check for BIO_new()

Add check for the return value of BIO_new() to avoid NULL pointer dereference.

Fixes: 0cd9dd703e ("Improve base64 BIO correctness and error reporting")
Signed-off-by: Jiasheng Jiang <jiashengjiangcool@gmail.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Frederik Wedel-Heinen <fwh.openssl@gmail.com>
MergeDate: Mon Jan 12 18:42:15 2026
(Merged from https://github.com/openssl/openssl/pull/27993)