This change import's upstream's beeb0fa7 and fixes a UAF in X509.
Thankfully, this shouldn't impact Chromium, which doesn't use OpenSSL
for certificate verification.
BUG=489764
Change-Id: I0ce2ec05083f7c588ba5504bb12151437dec593e
Reviewed-on: https://boringssl-review.googlesource.com/4810
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>