Fix issue if xarray/rioxarray dataset does not have a crs value

[niowniow]

Adds a check to the array_to_memory_file function that verifies if the crs provided by the array (from array.rio.crs) is not None.

Without it, there is no way to overwrite the crs using the keyword arguments of the array_to_memory_file function and as a consequence the given error message ("crs must be provided if source is not provided, such as EPSG:3857") is confusing because setting the crs argument has no effect.

Just for completeness, the current workaround would be to set crs before calling array_to_memory_file

array.rio.write_crs("EPSG:3857", inplace=True)