Fix fetching quote item by id

[mladenilic]

Description

Quote item without id (not yet saved) can be added to the collection. Even after being saved, it's still not possible to fetch it $this->getItemsCollection()->getItemById($itemId); as it was added before having the id.

Fixed Issues

1. Cart 860 does not contain item 1204 #9445: Cart 860 does not contain item 1204

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

All committers have signed the CLA.

[okorshenko]

Hi @mladenilic
Thank you for your contribution. Could you please cover you fix with integration test so that we can analyze the use case?

[okorshenko]

Hi @mladenilic. Could you please cover you fix with integration test so that we can analyze the use case and proceed with PR acceptance? Thank you

[mladenilic]

@okorshenko: Sure! Sorry, for not covering the change with the test initially.

I'll make sure I add the integration test later today.

Best,
Mladen