Candles can be placed on cakes while standing on the cake, despite this changing the hitbox

The bug

A candle can be placed on a cake, even if the player is standing directly on top of the cake. This is inconsistent with other placement, which requires the player to not be standing on the block for it to be placed.

Relates to MC-172901.

How to reproduce

1. Place down a cake
2. Stand on top of the cake
3. Place down a candle while looking down
4. Notice how the action succeeds, even though this action changes the hitbox of the cake and would normally not allow the player to stand in that space