core: fix poping messages from getLink methods when it's their only output

Author: iparamonau

lib/core.js

@@ -1205,7 +1205,7 @@
             }
 
             // Get message from plugin link.
-            if (!link.error) {
+            if (!link.error || link.error && link.message && Object.keys(link).length == 2) {
                 useMessage(result, link);
             }
         }