Slight improvement of error handling

- Do not try to reinitialize assets whose initialization failed.
- Fail gracefully when adding a scenegraphnode with a name that already exists

src/scene/asset.cpp

@@ -141,6 +141,10 @@ void Asset::requiredAssetChangedState(std::shared_ptr<Asset> child,
         // called more than once.
         return;
     }
+    if (state() == State::InitializationFailed) {
+        // Do not do anything if the asset failed to initialize.
+        return;
+    }
     if (childState == State::SyncResolved) {
         if (isSyncResolveReady()) {
             setState(State::SyncResolved);
@@ -154,10 +158,12 @@ void Asset::requestedAssetChangedState(std::shared_ptr<Asset> child,
                                        Asset::State childState)
 {
     if (child->hasInitializedParent()) {
-        if (childState == State::Loaded) {
+        if (childState == State::Loaded &&
+            child->state() == State::Loaded) {
             child->startSynchronizations();
         }
-        if (childState == State::SyncResolved) {
+        if (childState == State::SyncResolved &&
+            child->state() == State::SyncResolved) {
             child->initialize();
         }
     }

src/scene/scene.cpp

@@ -377,6 +377,12 @@ SceneGraphNode* Scene::loadNode(const ghoul::Dictionary& dict) {
     const std::string nodeName = dict.value<std::string>(KeyName);
     const bool hasParent = dict.hasKey(KeyParentName);
 
+    if (_nodesByName.find(nodeName) != _nodesByName.end()) {
+        LERROR("Cannot add scene graph node " << nodeName <<
+               ". A node with that name already exisis.");
+        return nullptr;
+    }
+
     SceneGraphNode* parent = nullptr;
     if (hasParent) {
         std::string parentName = dict.value<std::string>(KeyParentName);

src/scene/scene_lua.inl

@@ -359,7 +359,7 @@ int addSceneGraphNode(lua_State* L) {
     try {
         SceneGraphNode* node = OsEng.renderEngine().scene()->loadNode(d);
         if (!node) {
-            LERRORC("Could not load scene graph node", "scene");
+            LERRORC("Scene", "Could not load scene graph node");
             return luaL_error(L, "Error loading scene graph node");
         }