[bug] reordering of pasties does not persist when editing an existing paste

**describe the bug**
when editing an existing paste, reordering a pasty does not seem to remember those changes

**to reproduce**
steps to reproduce the behavior:
1. create a new paste with two or more pasties
2. once created, edit the paste
3. reorder pasties
4. save
5. view paste page. it does not save

**expected behavior**
custom order should be persistent when editing an existing paste

**screenshots**
n/a

**device and browser:**
- os: n/a
- browser: n/a
- browser version: n/a

**additional context**
n/a