Crossbows occasionally in the enchantment table will have low enchants at level 30

A crossbow in an enchantment table has a chance to get a low-level enchantment at level 30.

[Reproduce bug]

1. obtain a crossbow

2. go to an enchantment table

3. put the crossbow into the enchantment table

4. put 15 bookshelves around the enchantment table

5. if it does not appear try enchanting again