Guard SpawnItem against null CurrentMap and preserve inventory spawn behavior

[Copilot]

SpawnItem could throw a null reference when called before a map is initialized because it unconditionally read CurrentMap.Id. This change makes map assignment conditional on map-based spawning and safely no-ops when no current map exists.

• GameWorld spawn guard

  • Updated GameWorld.SpawnItem to only resolve CurrentMap.Id when:
    • no MapId is provided, and
    • item is not being spawned into an inventory.
  • If map-based spawn is requested with no initialized map, the method returns without spawning instead of throwing.

• Regression coverage

  • Added tests in SpawnGameObjectsTests for:
    • map-based spawn before map initialization (should not throw / should not spawn),
    • player-inventory spawn before map initialization (should still spawn into inventory).

• Behavioral intent

  • Map spawns require an initialized map context.
  • Inventory spawns remain independent of map lifecycle.

public void SpawnItem(SpawnItemParams spawnItemParams)
{
    if (spawnItemParams.MapId == Guid.Empty && spawnItemParams.Inventory == null && !spawnItemParams.IntoPlayerInventory)
    {
        if (CurrentMap == null)
            return;

        spawnItemParams.MapId = CurrentMap.Id;
    }

    Spawner.SpawnItem(spawnItemParams);
}