Don't unnecessarily perform block animations

@joe-goullaud minor fix

There is an issue with the collection view data source when an item gets updated. The normal batch update block also gets called, resulting in competing animations that don't layer correctly, and cells get stuck.

We may need to consider just removing the delayed item reload if anything else happened during the update - they don't seem to play nicely if two blocks are called in succession this way. Alternatively we could dispatch the update block until the next run loop to see if it makes a difference. I have a feeling it will just abort the in-progress animation.