Try using a single encoder thread to prevent stalling.

There may be a case where creation of encoder threads
causes a stall of the main thread, so instead of creating
a new encoder task queue for each connection, use a single thread
instead for encoding.  While this may load the thread more heavily
in some cases, Second Life only encodes a single stream even in
cross-region spatial situations, so a single thread should be sufficient
instead of starting/stopping threads each time a connection is needed.