SSL_apply_handback: don't choke on trailing data.

It may be useful for future extensibility.

Change-Id: I415095140367a44a2c8dd636998721399232c400
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/39964
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

ssl/handoff.cc

diff --git a/ssl/handoff.cc b/ssl/handoff.cc
index abe996b..3926939 100644
--- a/ssl/handoff.cc
+++ b/ssl/handoff.cc
@@ -671,8 +671,7 @@
       (hs->key_shares[0] = SSLKeyShare::Create(&key_share)) == nullptr) {
     return false;
   }
-
-  return CBS_len(&seq) == 0;
+  return true;  // Trailing data allowed for extensibility.
 }
 
 BSSL_NAMESPACE_END