Feather Search results: "Allow users to sort results" value is not persisted

[mirinka]

Steps to reproduce:

1. create page
2. drag and drop Search results widget
3. open designer
4. check "Allow users to sort results"
5. save widget settings
6. open designer again
   As a result: "Allow users to sort results" is not checked
   Note: verify sorting on frontend after this issue is fixed