GUAC-1101: Do not query accessible identifiers if none given.

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/glyptodon/guacamole/auth/jdbc/permission/ObjectPermissionService.java

@@ -233,6 +233,10 @@ public abstract class ObjectPermissionService
             ModeledUser targetUser, Collection<ObjectPermission.Type> permissions,
             Collection<String> identifiers) throws GuacamoleException {
 
+        // Nothing is always accessible
+        if (identifiers.isEmpty())
+            return identifiers;
+        
         // Determine whether the user is an admin
         boolean isAdmin = user.getUser().isAdministrator();