Thorns Is Incorrectly Available on Armor

Verification builds:
1.2.0.11 Retail

Summary:
When upgrading armour using the enchanting table, Thorns should only be available for Chestplates. Thorns for Leggings, Helmets and Boots should only be accessible using books and an anvil.

Steps to Reproduce:

1. Enchant a helmet, leggings, or boots

Observed Results:
Often, Thorns will be applied

Expected Results:
Thorns should only be available on Chestplates.

Screenshots/Videos attached: Yes

Notes:
For reference, see the table on the wiki page

See related ticket MCPE-23890