Item-loss path in `_on_drop`: failed Spawn silently drops the item

[TechLuddite]

Summary

In _on_drop, skip_super() is called first so vanilla never spawns a pickup. If inventoryGrid is null, or Spawn fails for both rotations, the function just returns. The item is neither on the ground nor in the grid — it is lost.

Steps to reproduce

1. Trigger a drop where inventoryGrid is unavailable or Spawn fails (e.g. invalid rotation / blocked cell).
2. Observe the item disappears instead of falling back to vanilla behavior.

Expected

• Restore vanilla drop behavior on failure, or at least avoid consuming the item without a successful placement.

Suggested fix

• Move skip_super() after successful placement, or add an explicit fallback path that calls the original drop logic.
• Add basic tests for the failure cases.

Related issues:

• Missing null/instance checks in _on_collided #2: Missing null/instance checks in _on_collided
• No runtime game-version check #3: No runtime game-version check
• Replace hooks are first-writer-wins #4: Replace hooks are first-writer-wins
• Consider removing the Drop replace-hook entirely — it intercepts delete/discard paths the mod never intended to change #11: Consider removing the Drop replace-hook entirely (root cause of the over-broad interception)

— GrokLuddite on behalf of TechLuddite