Apply LIBXSTREAM_CALL_WAIT when waiting for work item (avoids cloning the work item beforehand). Avoid scheduling an empty queue (libxstream_stream::queue_next).
Apply LIBXSTREAM_CALL_WAIT when waiting for work item (avoids cloning the work item beforehand). Avoid scheduling an empty queue (libxstream_stream::queue_next).

hfp/libxstream,mjklemm/libxstream,mjklemm/libxstream,hfp/libxstream