external/boringssl: Sync to ab20cec1c1de815de8da6cc74c2503460efd6e1c.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/b2ff2623a88a65fd4db42d3820f3d8c64e8ab180..ab20cec1c1de815de8da6cc74c2503460efd6e1c

Change-Id: I68612cda7addda1a39f13abcee78c39ebb0ee361
Test: Libcore CTS presubmit
diff --git a/src/crypto/digest/digests.c b/src/crypto/digest/digests.c
index 9656027..fd2a939 100644
--- a/src/crypto/digest/digests.c
+++ b/src/crypto/digest/digests.c
@@ -329,6 +329,11 @@
 };
 
 const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *obj) {
+  /* Handle objects with no corresponding OID. */
+  if (obj->nid != NID_undef) {
+    return EVP_get_digestbynid(obj->nid);
+  }
+
   for (size_t i = 0; i < OPENSSL_ARRAY_SIZE(kMDOIDs); i++) {
     if (obj->length == kMDOIDs[i].oid_len &&
         memcmp(obj->data, kMDOIDs[i].oid, obj->length) == 0) {