[Aggregate raster layer bands] wrong outputs for all-no-data inputs

[Andreas Rabe]

Reported by @Florian Katerndahl .

Some functions will return 0 or 1 if all inputs are no data. They should return no data.

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[Andreas Rabe]

Seams to be a bug in Numpy. Some nan-function do not return nan in case of nan inputs, e.g.

>>>np.nanprod([nan])
1.0
>>>np.nansum([nan])
0.0

I will mask out this cases manually.

[Andreas Rabe]

https://github.com/EnMAP-Box/enmap-box/commit/10db2397284224b5a5ef400602a2e14a08716d8d