backend/queue: Fix client disconnect
backend/queue: Fix client disconnect

When a client disconnects, it shall be removed from the queue.clients
map. Otherwise, the response channel will be closed twice (and thus
panic).

pythia-project/pythia-core,pythia-project/pythia-core,pythia-project/pythia-core,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia-core,pythia-project/pythia-core,pythia-project/pythia-core,pythia-project/pythia