llvmpipe: handle compute shader launch with 0 threads
If you set LP_NUM_THREADS=0 compute shaders would hang, just execute the workloads in sequence if we have no threads in the pool.
Fixes: 1b24e3ba ("llvmpipe: add compute threadpool + mutex")
If you set LP_NUM_THREADS=0 compute shaders would hang, just execute the workloads in sequence if we have no threads in the pool.
Fixes: 1b24e3ba ("llvmpipe: add compute threadpool + mutex")