[gltfio] Initialize mCgltfBuffersLoaded to fix crash (#7999)

Value of mCgltfBuffersLoaded is sometimes retained across creation of FAssetLoader which skips loading the buffer in AssetLoaderExtended#createPrimitive leading to null pointer crash

libs/gltfio/src/extended/AssetLoaderExtended.h

@@ -70,7 +70,8 @@ struct AssetLoaderExtended {
         : mEngine(engine),
           mGltfPath(config.gltfPath),
           mMaterials(materials),
-          mUriDataCache(std::make_shared<UriDataCache>()) {}
+          mUriDataCache(std::make_shared<UriDataCache>()),
+          mCgltfBuffersLoaded(false) {}
 
     ~AssetLoaderExtended() = default;