fix OER NULL and SEQUENCE extensions round-trip
diff --git a/skeletons/oer_encoder.c b/skeletons/oer_encoder.c
index 4b7d7da..1a691ed 100644
--- a/skeletons/oer_encoder.c
+++ b/skeletons/oer_encoder.c
@@ -136,6 +136,6 @@
     if(er.encoded < 0) return -1;
     assert(serialized_byte_count == (size_t)er.encoded);
 
-    return er.encoded + len_len;
+    return len_len + er.encoded;
 }