If copy fails, we shouldn't call cleanup. Also remove some pointless
NULL checks after EVP_PKEY_up_ref.
See also upstream's 748cb9a17f4f2b77aad816cf658cd4025dc847ee.
Change-Id: I2acb6892cde1ab662ca6a620d87179f9be609cba
Reviewed-on: https://boringssl-review.googlesource.com/13830
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>