fix(shared): Guard against exporting without settings

When generating a fully default design that does not require any
measurements, the export failed because where we expect a settings
object, we get `false` instead. This guards against this scenario by
instantiating an empty object in this case.

Fixes #5430

sites/shared/components/workbench/exporting/export-handler.mjs

@@ -114,6 +114,12 @@ export const handleExport = async ({
   // get a worker going
   const worker = new Worker(new URL('./export-worker.js', import.meta.url), { type: 'module' })
 
+  /*
+   * Guard against settings being false, which happens for
+   * fully default designs that do not require measurements
+   */
+  if (settings === false) settings = {}
+
   // listen for the worker's message back
   worker.addEventListener('message', (e) => {
     // on success