Move zeroing from bn_expand_internal() to bn_expand2() so that it happens reliably, even if the BIGNUM is already sufficiently large.
Move zeroing from bn_expand_internal() to bn_expand2() so that it
happens reliably, even if the BIGNUM is already sufficiently large.

[Note that the bn_expand()/bn_wexpand() macros call bn_expand2() only
if the BIGNUM actually has to grow, so this change does not add any
new overhead as currently bn_expand2() is never called directly.]

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl