Variables may have unreasonably large chunk sizes

[TonioF]

When opening a dataset, the chunk size can become very large too handle. We observed this for esacci.BIOMASS.yr.L4.AGB.multi-sensor.multi-platform.MERGED.1-0.r1 , where we got this chunk size:

The chunk size should be smaller, as a chunk size this large easily leads to an OutOfMemoryError.