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.
Can do the nil check up-front:
```lua
local paused_count = tonumber(pausedreqs:get(id_key)) or 0
```