crypto/bio/bio_print.c: avoid signed int overow in padlen calculation in fmtstr

crypto/bio/bio_print.c: avoid signed int overow in padlen calculation in fmtstr

In a highly unlikely situation of str being longer than INT_MAX,
a signed integer overflow in padlen calculation can be triggered.
Avoid it by reworking the check for the need of padlen calculation.

Fixes: 230c691a5218 "Fix fmtstr for BIO_printf() et al"
Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28502)