[BUG] Potentially undefined behavior of cuda_stream_pool::get_stream

[achirkin]

These functions seem to have the undefined behavior (remainder of zero division) for the case when the pool size is zero (which is the default in raft::handle_t and as such is rather dangerous):

rmm/include/rmm/cuda_stream_pool.hpp

Lines 61 to 64 in fe53a72

	rmm::cuda_stream_view get_stream() const noexcept
	{
	return streams_[(next_stream++) % streams_.size()].view();
	}

rmm/include/rmm/cuda_stream_pool.hpp

Lines 76 to 79 in fe53a72

	rmm::cuda_stream_view get_stream(std::size_t stream_id) const
	{
	return streams_[stream_id % streams_.size()].view();
	}

[jrhemstad]

Hm, we should probably disallow constructing with a pool size of 0. I can't think of a sane behavior of get_stream when the pool is empty.