Error catching when preloading fails does not work

Hi,

It seems the code to catch missing id on preloading and translate it into a KError to generate a 404 status does not work (and I actually get a 500 status in this case).

Typically, in the server/controllers/v1/accounts.js file, there are these lines which, as far as I understood, should translate the missing account into a 404 response from the API:

let account = await Account.find(accountID);
if (!account) {
    throw new KError('Bank account not found', 404);
}

It does not seem to work as Account.find raises its own exception when not finding an accountID and the if test is completely ignored then. At least, in my server logs, I have:

[2017-08-06 02:48:36:51] error - helpers | when preloading a bank account: missing
[2017-08-06T14:48:36.520Z] GET /api/v1/accounts/26f74985558c4655a68af8b6e171e819/operations - 500 (8.926 ms)

with no other occurrences of missing in the code than in the cozy-db client.