Apply upstream revision 3612ff6fcec0e3d1f2a598135fe12177c0419582:

Fix overflow check in BN_bn2dec()
Fix an off by one error in the overflow check added by 07bed46
("Check for errors in BN_bn2dec()").

This fixes a regression introduced in SA-16:26.openssl.

Submitted by: jkim
PR: 212921