Id map clean-up

[radarfox]

Hello Jason,

I have found a bug / performance tweak in this adapter. It causes saving unnecessary data in storage.

Conditions:

• create new empty resource with this adapter
• call find or findAll or destroyAll

OR

• have a last item in resource
• call destroy on in

Result:

Unnecessary id map for resource with value {} is created in localstorage.

I dont like it because:

• it is slowing down my app initialization (async create for each resource)
• it is lowering my localstorage data limit, especially when using longer endpoint/resource name
• it is making debug harder because of long list of localstorage data, so I have to scroll and look what "real" data are stored

I think that the problem is in this line https://github.com/js-data/js-data-localstorage/blob/master/dist/js-data-localstorage.js#L159

[radarfox]

Works like a charm. Thanks much for the quick fix.