dht: fail pending readiness on shutdown and teardown

src/dht.cpp

@@ -83,6 +83,7 @@ Dht::shutdown(ShutdownCallback cb, bool stop)
                         cb(false, {});
                 }
                 sr.second->announce.clear();
+                sr.second->cache.onReady(false);
                 sr.second->listeners.clear();
             }
         }

src/search.h

@@ -851,6 +851,7 @@ struct Dht::Search
 
     void clear()
     {
+        cache.onReady(false);
         announce.clear();
         callbacks.clear();
         listeners.clear();