fix: repair after broken join

The bug that caused broken joins was fixed here:
a5f004d7e9

But that commit doesn't repair those joins afterwards because the broken
join event is still in the auth chain. This commit will leave out the
the member join event from the auth_events in leave->* transitions.

Also see https://github.com/matrix-org/matrix-doc/issues/3695

src/database/rooms.rs

@@ -295,6 +295,22 @@ impl Rooms {
                 sauthevents.remove(&shortstatekey).map(|k| (k, event_id))
             })
             .filter_map(|(k, event_id)| self.get_pdu(&event_id).ok().flatten().map(|pdu| (k, pdu)))
+            .filter(|(_, pdu)| {
+                if pdu.kind != EventType::RoomMember {
+                    return true;
+                }
+
+                #[derive(Deserialize)]
+                struct ExtractMembership {
+                    membership: MembershipState,
+                }
+
+                // Leave out auth events where the membership is leave
+                match serde_json::from_str::<ExtractMembership>(pdu.content.get()) {
+                    Ok(e) => e.membership != MembershipState::Leave,
+                    Err(_) => true,
+                }
+            })
             .collect())
     }