List does not remain sorted after adding a new show

[Ashuh]

When the add command is used after the sort command, the ordering of the list as per the previous sort command is no longer obeyed.

Steps to recreate:

1. Sort the list. e.g., sort r/asc
2. Add a new show. e.g., add n/Crime Watch s/completed r/0

Expected:

The list should still be sorted by rating, as shown in this image

Actual:

The new show is added at the end of the list, as shown in this image