Only call `frame_split_size` when there are frames (#3996)
Only call `frame_split_size` when there are frames (#3996)

This just becomes a no-op if an empty list is given (returning an empty
list). However there is no need to do this work if we don't need it. So
simply restrict calling `frame_split_size` to the case where frames are
present and compression will occur.
dask/distributed,dask/distributed,dask/distributed,dask/distributed