events: try nostrdb cache if we don't have one in-memory

Our nip10 logic looks for notes only in the in-memory cache. This means
sometimes threads don't get fully loaded if for whatever reason it's in
the nostrdb cache but not in-memory.

Ideally we would just remove our in-memory cache, but for now let's just
hack it so it falls back to nostrdb and makes an owned note.

Changelog-Fixed: Fixed threads not loading sometimes
Signed-off-by: William Casarin <jb55@jb55.com>

damus/Util/EventCache.swift

@@ -218,7 +218,16 @@ class EventCache {
      */
 
     func lookup(_ evid: NoteId) -> NostrEvent? {
-        return events[evid]
+        if let ev = events[evid] {
+            return ev
+        }
+
+        if let ev = self.ndb.lookup_note(evid)?.unsafeUnownedValue?.to_owned() {
+            events[ev.id] = ev
+            return ev
+        }
+
+        return nil
     }
     
     func insert(_ ev: NostrEvent) {