Modules: fix shared dict state JSON separators

Modules: fix shared dict state JSON separators

When saving a shared dict zone with timeout=, expired entries are
skipped.  A comma is appended whenever another tree node follows a live
entry, even if all remaining nodes are expired.  This can leave a
trailing comma in the state file, making it invalid JSON.

Insert commas before live entries only when a previous entry has been
rendered, so skipped entries do not affect the separators.