ts: fix exception class raised when getting an OID name

get_asn1obj() is used by several methods in OpenSSL::Timestamp to get
the string representation of an OID. On an error, such as memory
allocation failure, it can raise OpenSSL::X509::AttributeError. It
should be OpenSSL::Timestamp::TimestampError instead.

Author: rhenium

ext/openssl/ossl_ts.c

@@ -161,8 +161,11 @@ get_asn1obj(ASN1_OBJECT *obj)
         ret = rb_str_new2(OBJ_nid2sn(nid));
     else{
         if (!(out = BIO_new(BIO_s_mem())))
-            ossl_raise(eX509AttrError, NULL);
-        i2a_ASN1_OBJECT(out, obj);
+            ossl_raise(eTimestampError, "BIO_new(BIO_s_mem())");
+        if (i2a_ASN1_OBJECT(out, obj) <= 0) {
+            BIO_free(out);
+            ossl_raise(eTimestampError, "i2a_ASN1_OBJECT");
+        }
         ret = ossl_membio2str(out);
     }