The store does not handle concurrent calls well

Expected behavior

When a call is made to a resource while all its children have not been cached completely, the store returns null values

What's happening?

Here is a timeline of what's happening:

1. component1 loads matthieu/circles/

   • caching matthieu/circles
   • caching circle-members/1
   • caching circle-members/2
   • ...

2. component2 asks for matthieu/circles -> already in the cache, container returned

   • iterate on resources of the container
   • get circle-members/1 -> returned from the cache
   • get circle-members/2 -> returned from the cache
   • get circle-members/3 -> not in the cache, return null

3. component1 still loading

   • caching circle-members/3
   • resolve and return

Steps to reproduce

In a page with core@0.10, execute this script:

      document.addEventListener('DOMContentLoaded', async() => {
        const context = {
          '@vocab': 'http://happy-dev.fr/owl/#',
          ldp: 'http://www.w3.org/ns/ldp#',
        };

        store.getData("https://api.test1.startinblox.com/users/", context).then(() => {
          const userProfile = store.get('https://api.test1.startinblox.com/users/jbpasquier/')
          return userProfile['circles'];
        }).then(() => {
          console.log(store.cache.get('https://api.test2.startinblox.com/circle-members/22/'))
        });

        setTimeout(() => {
          console.log(store.get('https://api.test1.startinblox.com/users/jbpasquier/circles/')['ldp:contains'])
        }, 500);
      })

You will see the second log appear first. An array with 2 proxies and 1 null will be displayed, because the 3rd resource is distant and not included in the container. When the log happens, the request to fetch it is still loading. You may have to adjust the timeout to see it.