steam-http: fixed the paused request queue

Currently, requests that are queued for resending when the queue is
paused are immediately sent as well as requeued. This is problematic,
as they are resent without the STEAM_HTTP_REQ_FLAG_NOFREE flag, and
this inevitably leads to segmentation faults. Moreover, the whole
resending logic needed a bit of refactoring.

This fixes the client crashing upon the relogon operation.