multiple reads of nasa-nex-gddp-cmip6 dataset from MultiZarrToZarr concatenated metadata returns all nans

Simply running twice cells 13 & 14 of the notebook that read and plot point single variable time-series for a point will reproduce this issue where the first run will have the valid values but second will be all nans. I encountered this when parallelizing reading of the files with dask that results in multiple reads and the unexpected result.

從 datasets/nasa-nex-gddp-cmip6/nasa-nex-gddp-cmip6-example.ipynb 中的儲存格 13 和 14 開始，重現兩次點時間序列讀取。檢查 MultiZarrToZarr 串接中繼資料的行為，包括重複讀取或平行讀取。完成的標準是第二次讀取返回與第一次相同的有效值，而不是全部為 NaNs。