Emit children if it wasn't collected.

Align node's `children` with `value`, where emitted field means didn't try to get the value.

Author: Maksim Sadym

index.bs

@@ -2082,7 +2082,7 @@ an |ownership type|, a |serialization internal map|, a |realm| and a |session|:
 
             1. Append |serialized| to |children|.
 
-          1. Set |serialized|["<code>children</code>"] to |children|.
+          1. If |children| is not null, set |serialized|["<code>children</code>"] to |children|.
 
           1. If |value| is an [=/Element=]: