Attempt to GET "undefined" on creating a widget

Overview:

In console when creating a simple search widget instance on the dashboard, when the widget is saved there is a GET to /servint/widgets/instances/undefined

curl 'https://folio-snapshot-okapi.dev.folio.org/servint/widgets/instances/undefined' \
  -H 'authority: folio-snapshot-okapi.dev.folio.org' \
  -H 'accept: application/json' \
  -H 'x-okapi-tenant: diku' \
  -H 'x-okapi-token: <token>' \
  -H 'origin: https://folio-snapshot.dev.folio.org' \
  -H 'sec-fetch-site: same-site' \
  -H 'sec-fetch-mode: cors' \
  -H 'sec-fetch-dest: empty' \
  -H 'referer: https://folio-snapshot.dev.folio.org/' \
  -H 'accept-language: en,en-US;q=0.9,en-GB;q=0.8' \
  --compressed

This results in a 403 response

{
  "timestamp": 1622026677394,
  "status": 403,
  "error": "Forbidden",
  "message": "Forbidden",
  "path": "/servint/widgets/instances/undefined"
}

Dev task breakdown

• I expect a combination of this and this are causing this behaviour
• Need to ensure we aren't getting memoized version on next edit (Whatever the solution)
• Check removing from 'post' is sufficient, and that that doesn't cause unwanted behaviour on next edit(s)
  • Will need testing with a single widget, and also editing another widget after posting

• If unwanted behaviour occurs, will perhaps need state variable containing `params.id` || id gained from post, with that replacing the last variable in the fetch.
• Hopefully won't be needed, as that would be messy