namedirectory: prevent deadlock on destruction

The default status code of 0 is passed to the done callbacks when
the requests are destroyed. Returning from the callback when we get
this code prevents locking the mutex on multiple times on the same
thread.

Change-Id: I4e6da6de7b6572d6a0f744c3b90d1be28ad0298c

src/jamidht/namedirectory.cpp

@@ -162,6 +162,9 @@ NameDirectory::lookupAddress(const std::string& addr, LookupCallback cb)
         setHeaderFields(*request);
         request->add_on_done_callback(
             [this, cb = std::move(cb), reqid, addr](const dht::http::Response& response) {
+                if (response.status_code == 0) {
+                    return;
+                }
                 if (response.status_code >= 400 && response.status_code < 500) {
                     cb("", Response::notFound);
                 } else if (response.status_code != 200) {
@@ -248,6 +251,9 @@ NameDirectory::lookupName(const std::string& n, LookupCallback cb)
         setHeaderFields(*request);
         request->add_on_done_callback([this, reqid, name, cb = std::move(cb)](
                                           const dht::http::Response& response) {
+            if (response.status_code == 0) {
+                return;
+            }
             if (response.status_code >= 400 && response.status_code < 500)
                 cb("", Response::notFound);
             else if (response.status_code < 200 || response.status_code > 299)