src: return UV_EAI_NODATA on empty lookup

AfterGetAddrInfo() can potentially return an empty array of
results without setting an error value. The JavaScript layer
expects the array to have at least one value if an error is
not returned. This commit sets a UV_EAI_NODATA error when an
empty result array is detected.

Fixes: https://github.com/nodejs/node/issues/4545
PR-URL: https://github.com/nodejs/node/pull/4715
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

src/cares_wrap.cc

@@ -983,6 +983,10 @@ void AfterGetAddrInfo(uv_getaddrinfo_t* req, int status, struct addrinfo* res) {
       address = address->ai_next;
     }
 
+    // No responses were found to return
+    if (n == 0) {
+      argv[0] = Integer::New(env->isolate(), UV_EAI_NODATA);
+    }
 
     argv[1] = results;
   }