fix IGListKit updates logging
fix IGListKit updates logging

Summary:
* Issue: we don't log the IGListKit updates
* Cause: IGListAdapterUpdater clears the ongoing updates before we call the delegate (https://fburl.com/76w5wvpl)
* Fix: keep a hold of the updates before calling executeCompletionBlocks(...)

Reviewed By: rnystrom

Differential Revision: D6750327

fbshipit-source-id: a30572873ab753b067977288cdb465a2a222e715

Instagram/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,zhubofei/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,Instagram/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,zhubofei/IGListKit