Add EVP_EncodedLength.

Several callers of EVP_EncodeBlock are doing ad-hoc versions of this
function without any overflow checks.

Change-Id: I4d0cad2347ea8c44b42465e8b14b2783db69ee8f
Reviewed-on: https://boringssl-review.googlesource.com/1511
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
5 files changed