SetMemoRelations(...) can insert duplicated/wrong relation.

[harveyghq]

Describe the bug

When modifiy a related memo/comment, current SetMemoRelations v2 api inserts the existed relation again, violating the constraints on memo_relation table. If the requested memo id equals the related id in state.relationList, a reflexive relation can be inserted, which obviously isn't correct.

Steps to reproduce

1. Write a comment C under a memo A (in memo detail page).
   2.1 Modify the comment C, which fails due to a duplicated insertion.
   2.2 Modify the memo A, refresh the page, and the relations go to a mess due to a reflexive insertion.

The version of Memos you're using

0.18.2

Screenshots or additional context