This fixes uninitialized memory read reported by Nick Mathewson in
https://github.com/openssl/openssl/issues/6347.
It imports the memset from upstream's 2c739f72e5236a8e0c351c00047c77083dcdb77f,
but I believe that fix is incorrect and instead RC4 shouldn't be allowed in
this context. See
https://github.com/openssl/openssl/pull/6603#issuecomment-413066462 for
details.
Update-Note: Decoding a password-protected PEM block with RC4 will, rather than
derive garbage from uninitialized memory, simply fail. Trying to encode a
password-protect PEM block with an unsupported cipher will also fail, rather
than output garbage (e.g. tag-less AES-GCM).
Change-Id: Ib7e23dbf5514f0a523730926daad3c0bdb989417
Reviewed-on: https://boringssl-review.googlesource.com/31084
Reviewed-by: Adam Langley <agl@google.com>
