Item modifiers that change the count to 0 don't completely remove the item

The bug

When subtracting from the count of an item with /item ... modify and it reaches 0, it isn't completely removed. This happens both on entities and containers.

How to reproduce

1. Add the data pack MC-205627.zip to the world and /reload
2. Place any item in the first hotbar slot

3. /item entity @s hotbar.0 modify test:remove_count

4. /item entity @s hotbar.0 modify test:add_count

5. Notice that the original item is back. If you had relogged between step 3 and 4 this would have failed.