untagged-8d08ed3344379bb4c08d: Fixed gateways generating half of themselves 48 blocks lower

-Fixed length and height being swapped in Cubic Chunks Schematic Placement (stumbled upon this
-Fixed gateways partially generating at y level 16 if the (cubic) chunk they *should* be in was totally empty / 100% air (storage = null), because yBase wasn't taken into account.