Shulkers open into blocks when unable to teleport.

What I expected to happen was...:
The shulker should have been unable to open into a block.

What actually happened was...:
The shulker continued to open, clipping into the block in the path of its shell opening.

Steps to Reproduce:

1. Place a block high enough in the air that the shulker cannot teleport to any other blocks in the area.
2. Cover all sides of the block except the top with buttons.
3. Place a block above the current block with one block of air between.
4. Cover all sides of that block except the bottom with buttons.
5. Spawn a shulker on the top face of the bottom block and observe for a few seconds.