in an empty Kreate

• put a compacting upgrade in an upgrade slot, set it to 3x3 mode
• put an iron block in the last slot
• put a stack of iron in the first slot

when the compacting upgrade creates new iron blocks it should add them to the first non-full stack of iron blocks, not just place them in the first empty slot.

obviously this is a pathalogical repro case, but if you have a sluice piping many types of items into a Krate then, over time, you end up with duplicate partial stack of input items, and duplicate partial stacks of compacted items, wasting a ton of space and causing the Krate to reject items well before it's actually full.