Ensure guardfiles are removed even when an exception is raised

I have had intermittent issues with orphaned guard files preventing any delta indexing from happening via Sidekiq. I suspect that Sidekiq jobs are crashing or Sidekiq is restarting due to a deploy, etc. Some delta jobs take more than a few minutes, and Sidekiq only gives running jobs 8 seconds to complete. 

I added an ensure block to the index to force cleanup of the guard files no matter what.