GetNextIdValue should return next id based on the largest id in the collection, not based on the last item's id

[ttu]

GetNextIdValue checks only the last item from the collection and gives a new id based on that item's id. Method should find the item with the largest id value from the collection and give a new id based on that item's id.

Function is in JsonFlatFileDataStore/DocumentCollection.cs
Tests are in JsonFlatFileDataStore.Test/CollectionTests.cs

[loneshark99]

I would like to take this item. Can I ?

[ttu]

@loneshark99 sure! If you have some questions, just ask. I will add in progress label, but there is no hurry to complete this task.

[ttu]

@loneshark99 Hi. Do you have any questions regarding this task or if you are not anymore interested in implementing this, just tell me and I will remove "In Progress" label.

[qpooqp]

Hi.
I stumbled upon this issue and tried to solved it.
Can you look on last commit on my fork if it looks okay? Or should I make PR?

I must admit that it is probably not the most eficient solution, but i couldn't come up with better one

[ttu]

Thanks! Just make the PR and we can then think together if there is some more efficient way.