fix(lxlweb): don't crash in getHeldBy on missing org

[andersju]

I noticed occasional 500 errors in prod:

[500] GET /find?_q=something&_cursor=15&_limit=20&_offset=0&_sort=&_spell=true
TypeError: Cannot read properties of undefined (reading '_members')
    at getHeldBy (file:///data/packages/lxlweb-4001/build/server/chunks/holdings-BAo2QGfb.js:105:38)
    at getHeldByLibraries (file:///data/packages/lxlweb-4001/build/server/chunks/search.server-DWX7h352.js:505:13)
    at file:///data/packages/lxlweb-4001/build/server/chunks/search.server-DWX7h352.js:271:28
    at Array.map (<anonymous>)
    at asSearchResultItem (file:///data/packages/lxlweb-4001/build/server/chunks/search.server-DWX7h352.js:262:17)
    at asResult (file:///data/packages/lxlweb-4001/build/server/chunks/search.server-DWX7h352.js:239:12)
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
    at async load (file:///data/packages/lxlweb-4001/build/server/chunks/11-B1mPktAO.js:93:24)
    at async fn (file:///data/packages/lxlweb-4001/build/server/index.js:1266:23)
    at async load_server_data (file:///data/packages/lxlweb-4001/build/server/index.js:1257:18)

The problem is that getHeldBy assumes that every org in a user's myLibraries has a matching entry in orgs, but this is not necessarily true, as orgs is the result of getRefinedOrgs(libraries) which keeps only those for which isLibraryOrg is true.

This can happen if the user has favorited an org with no member libraries (if that's possible...?), or if the org (which is stored in a cookie) has been deleted or renamed, or possibly (at startup) due to a race condition if refreshLibraries hasn't finished.

Anyway, for the unlucky visitor this results in virtually all search result pages and individual records simply crashing with a 500 error, until that cookie is cleared. So let's fix that.

[kaipoykio]

looks good

[andersju]

On closer inspection the 500s I saw were probably because refreshLibraries had failed on a couple of the servers, which in turn triggered this. But this fix is still valid, and I'll make a separate PR to make refreshLibraries more robust.