In DNS lookup code, make sure the weak pointer we use lives through the expected scope (if branch)

ws/CMakeLists.txt

@@ -54,6 +54,7 @@ add_executable(ws
   ws_redis_publish.cpp
   ws_redis_subscribe.cpp
   ws_cobra_subscribe.cpp
+  ws_cobra_metrics_publish.cpp
   ws_cobra_publish.cpp
   ws_cobra_to_statsd.cpp
   ws_cobra_to_sentry.cpp