Update utglTF2ImportExport.cpp

Check scene pointer against nullptr.

test/unit/utglTF2ImportExport.cpp

@@ -371,6 +371,7 @@ TEST_F(utglTF2ImportExport, importglTF2FromMemory) {
         aiProcess_FindDegenerates | aiProcess_GenUVCoords | aiProcess_SortByPType;
     const auto& buff = ReadFile("C:\\Users\\kimkulling\\Downloads\\camel\\camel\\scene.gltf");
     const aiScene* Scene = ::aiImportFileFromMemory(&buff[0], buff.size(), flags, ".gltf");
+    EXPECT_NE( nullptr, Scene );
 }
 
 #ifndef ASSIMP_BUILD_NO_EXPORT