fix: Washing activity now appropriately adds item if split.

[KheirFerrum]

Purpose of change (The Why)

• fixes Filthy leather patches disappear after cleaning #6024, which is due to the washing activity working fine if an item is washed all at once but doesn't spawn the split portion of an item if they are only partially washed.

Describe the solution (The How)

• Make the washing activity actually spawn the item it generates for the split.

Describe alternatives you've considered

Testing

• Spawn 2 filthy leather patches and appropriate amounts of detergent/water/washboard
  • Washing only 1 leaves you with 1 clean and 1 dirty.

Additional context

Checklist

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