Boats do not block the rendering of fluids inside cauldrons

The bug

While boats will stop water from rendering if said water exists within the world, the same does not happen for water placed in cauldrons, resulting in water being able to appear in the boat.

How to reproduce

1. Place a cauldron
2. Fill the cauldron with water
3. Place a slab next to the cauldron
4. Place a boat on the slab
5. Make the boat intersect the cauldron visually

Expected results

The water inside of the cauldron would not render inside of the boat.

Actual results

It does.

Further notes

This may fix itself if MC-13187 is fixed.