Nodes with zero population are wrongly assigned diesel mini-grid technology

[shakythesherpa]

Any node in the input demographic file with a zero population is by default assigned a diesel mini-grid system. Although when you look at the costs it is obvious that there is no calculations that happen when the population is zero it may be confusing to assign the node a specific technology. May be we should stick to the old system and label it "unelectrified" or flag it with some other keywords.