Print out zero length string properly.

crypto/asn1/tasn_prn.c

@@ -506,7 +506,8 @@ static int asn1_print_obstring_ctx(BIO *out, ASN1_STRING *str, int indent,
 		}
 	else if (BIO_puts(out, "\n") <= 0)
 		return 0;
-	if (BIO_dump_indent(out, (char *)str->data, str->length,
+	if ((str->length > 0)
+		&& BIO_dump_indent(out, (char *)str->data, str->length,
 				indent + 2) <= 0)
 		return 0;
 	return 1;