Fbx scene re-import is not marking as dirty new asset

Make sure all created and modified asset in a re-import are mark dirty. Creating a collision mesh was dirtying the asset, this is why the bug is only when we are not generating collision mesh.

1. Export a FBX file with at least 1 object.
2. In Unreal, go to File>Import Into level, and simply import with the default options.
3. Save the imported files
4. Go back to the 3D app and add a new box, and export the FBX file again.
5. In Unreal, right click the FBX scene import data file and choose Reimport.
6. Under the Static mesh tab in the reimport options, make sure Auto Generate Collision is turned off. Click Reimport.
7. In the Content Browser, look at the static meshes. Notice that all object has the "unsaved" star, except for the newly added box?
8. Save anyway. Close and start the project again.
9. Now you'll be greeted with messages about how Unreal couldn't find the newly added box.
10. Also, if you look in the project folder in explorer, the box isn't there either.