Fix crash when using image-based textures.

Image lights are not normal lights, so use nullptr as a placeholder.
Add checks for nullness when iterating over the lights.

PiperOrigin-RevId: 840695579
Change-Id: I092515ae814523e85f4f5ce87b2bac2241f4ea35

src/experimental/filament/filament/scene_view.cc

@@ -327,11 +327,13 @@ void SceneView::PrepareLights() {
     SetFallbackEnvironmentLight(kFallbackEnvironmentLightIntensityCandela);
     const float intensity = kTotalSceneLightIntensityCandela / lights_.size();
     for (auto& light : lights_) {
+      if (light) {
         light->SetIntensity(light->IsHeadlight() ? kHeadlightIntensityCandela
                                                 : intensity);
       }
     }
   }
+}
 
 void SceneView::UpdateScene(const mjrContext* context, const mjvScene* scene) {
   mjtNum hpos[3], hfwd[3];
@@ -381,9 +383,11 @@ void SceneView::UpdateScene(const mjrContext* context, const mjvScene* scene) {
       continue;
     } else if (scene_light.id < lights_.size() - 1) {
       std::unique_ptr<Light>& light = lights_[scene_light.id];
+      if (light) {
         light->SetColor(ReadFloat3(scene_light.diffuse));
         light->SetTransform(ReadFloat3(scene_light.pos),
                             ReadFloat3(scene_light.dir));
+      }
     } else {
       mju_error("Unexpected light id: %d", scene_light.id);
     }