We've never allowed this as no good can come of it. Add a test for this.
Change-Id: I4b92372f58c1fe2054e33007adbe496d153a9251
Reviewed-on: https://boringssl-review.googlesource.com/14266
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>