Fix bug where no paused requests would throw an exception

We have to ensure id isn’t nil, so after we interrogate
`pausedreqs:get(id_key)`, we check that our result (`id`) is not nil.
If it is, set the result (`id`) to 0, and continue.
Fix to make setting/nil checking paused_count a one-liner
Merge pull request #4 from basecamp/fix-no-paused-requests-bug

Fix bug where no paused requests would throw an exception