external/boringssl: cherry-pick crash fix

This change cherry-picks the following change from upstream:

commit 61dedd681501616de5928fe5c0eac6640d4de0c1
Author: Adam Langley <alangley@gmail.com>
Date:   Wed Feb 7 14:59:44 2018 -0800

    Don't crash when failing to set affine coordinates when the generator is missing.

    If a caller is in the process on constructing an arbitrary |EC_GROUP|,
    and they try to create an |EC_POINT| to set as the generator which is
    invalid, we would previously crash.

    Change-Id: Ida91354257a02bd56ac29ba3104c9782b8d70f6b
    Reviewed-on: https://boringssl-review.googlesource.com/25764
    Commit-Queue: David Benjamin <davidben@google.com>
    Reviewed-by: David Benjamin <davidben@google.com>
    CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Change-Id: I27fc13f2bb2538b7f9621d94438653e58ee79e7b
Test: has been running internally for several weeks without issue.
1 file changed