Windmills always span more than one mapblock, so even with a switching station next to the generators, they will stop working if unloaded due to the windmill check failing to handle CONTENT_IGNORE of the frames at the foot of the windmill, unless a second switching station would be placed there.
The commit assumes, that a user has to load a block to modify it, and thus unloaded blocks to have the same windmill frame state as before.
This also makes technic_run for windmills a little faster by being able to skip some unnecessary node lookups and generally avoiding creation of 20 tables per windmill per step.
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