Sync operations sometimes do not align

[kegsay]

In cases where you have two lists:

• one tracking all rooms
• one tracking visible rooms

You would expect index positions to match up if they are using the same filters (which they are). In practice this does not seem to always happen:

{
  "all_rooms": SyncList {
    ops: [
      SyncOp { op: Delete, range: None, index: Some(5), room_ids: [], room_id: None },
      SyncOp { op: Insert, range: None, index: Some(0), room_ids: [], room_id: Some("!kCCQTCfnABLKGGvQjo:matrix.org") 
    }],
    count: 4014
  }, "invites": SyncList {
    ops: [], count: 181
  }, "visible_rooms": SyncList {
    ops: [
      SyncOp { op: Delete, range: None, index: Some(6), room_ids: [], room_id: None }, 
      SyncOp { op: Insert, range: None, index: Some(0), room_ids: [], room_id: Some("!kCCQTCfnABLKGGvQjo:matrix.org") 
    }],
    count: 4014
  }
}

or sometimes one list just doesn't have it as an operation at all:

lists={
  "all_rooms": SyncList { ops: [], count: 4014 }, 
  "invites": SyncList { ops: [], count: 181 }, 
  "visible_rooms": SyncList { ops: [SyncOp { op: Delete, range: None, index: Some(11), room_ids: [], room_id: None }, SyncOp { op: Insert, range: None, index: Some(0), room_ids: [], room_id: Some("!zAeWUNBoXONgkVtgqn:mozilla.org") }], count: 4014 }
}

Possibly related to #192 as this will cause DB hits to sometimes see the user as joined, sometimes not.