Per ecdsa(3ssl), ECDSA_SIG_new does allocate its 'r' and 's' bignum fields.
Fix a bug where the initial 'r' and 's' bignums were being overwritten with
newly-allocated bignums, resulting in a memory leak.
BUG: https://red.libssh.org/issues/175
Signed-off-by: Jon Simons <jon@jonsimons.org>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
(cherry picked from commit 4745d652b5)