Fix internal error on pin/unpin

[AvoidMe]

Solves: #4331

Seems like query in UpdateMemo is empty, because pin/unpin actually updates only memo_organizer table.

		} else if path == "pinned" {
			if _, err := s.Store.UpsertMemoOrganizer(ctx, &store.MemoOrganizer{
				MemoID: id,
				UserID: user.ID,
				Pinned: request.Memo.Pinned,
			}); err != nil {
				return nil, status.Errorf(codes.Internal, "failed to upsert memo organizer")
			}

Not sure if this is how maintainers wants to solve it, this is first time I'm looking at memos code.
But I'm willing to improve/rewrite pr if any changes requrired.

[johnnyjoygh]

LGTM