Check for ambientLightingThread non-null before use (#11590)

src/modules/ExternalNotificationModule.cpp

@@ -247,7 +247,9 @@ void ExternalNotificationModule::setExternalState(uint8_t index, bool on)
         blue = 0;
         white = 0;
     }
-    ambientLightingThread->setLighting(moduleConfig.ambient_lighting.current, red, green, blue);
+    if (ambientLightingThread) {
+        ambientLightingThread->setLighting(moduleConfig.ambient_lighting.current, red, green, blue);
+    }
 #endif
 
 #ifdef HAS_DRV2605