light: stop the update request from running twice

In case the rgb+white(cct) brightness function was selected by the
configuration, internal calculations will always result in 'changed' being 'true'
and as a result it will continiously re-create the transition object.

fix #2467 (at least for now, the brightness function should be actually fixed)

code/espurna/light.cpp

@@ -1333,6 +1333,7 @@ struct LightUpdateHandler {
     template <typename T>
     void run(T&& callback) {
         if (_run) {
+            _run = false;
             LightUpdate update{_update};
             callback(update.save, update.transition, update.report);
         }