Always check that the value returned by asn1_do_adb() is non-NULL.

(Imported from upstream's a9b23465243b6d692bb0b419bdbe0b1f5a849e9c,
5e102f96eb6fcdba1db2dba41132f92fa492aea0, and
9bda72880113b2b2262d290b23bdd1d3b19ff5b3.)

Change-Id: Ib608acb86cc128cacf20811c21bf6b38b0520106
Reviewed-on: https://boringssl-review.googlesource.com/8944
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

crypto/asn1/tasn_dec.c

diff --git a/crypto/asn1/tasn_dec.c b/crypto/asn1/tasn_dec.c
index 616b587..dfbd222 100644
--- a/crypto/asn1/tasn_dec.c
+++ b/crypto/asn1/tasn_dec.c
@@ -399,7 +399,9 @@
             if (tt->flags & ASN1_TFLG_ADB_MASK) {
                 const ASN1_TEMPLATE *seqtt;
                 ASN1_VALUE **pseqval;
-                seqtt = asn1_do_adb(pval, tt, 1);
+                seqtt = asn1_do_adb(pval, tt, 0);
+                if (seqtt == NULL)
+                    continue;
                 pseqval = asn1_get_field_ptr(pval, seqtt);
                 ASN1_template_free(pseqval, seqtt);
             }
@@ -410,7 +412,7 @@
             const ASN1_TEMPLATE *seqtt;
             ASN1_VALUE **pseqval;
             seqtt = asn1_do_adb(pval, tt, 1);
-            if (!seqtt)
+            if (seqtt == NULL)
                 goto err;
             pseqval = asn1_get_field_ptr(pval, seqtt);
             /* Have we ran out of data? */
@@ -475,7 +477,7 @@
         for (; i < it->tcount; tt++, i++) {
             const ASN1_TEMPLATE *seqtt;
             seqtt = asn1_do_adb(pval, tt, 1);
-            if (!seqtt)
+            if (seqtt == NULL)
                 goto err;
             if (seqtt->flags & ASN1_TFLG_OPTIONAL) {
                 ASN1_VALUE **pseqval;