Why is there a warning and not an error when method `open3d.io.read_point_cloud` cannot read the file?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `main` branch).

### My Question

At the moment, it is not possible to save a point cloud of size 0; accordingly, you can check whether the file has been read based on the number of points or use package `os` to make sure that the file exists. On the other hand, in most situations I've come across, as soon as I don't find the file, I throw an error because my program won't work correctly with an empty file. If the absence of a file is not a problem for some user, then he can use `try-exept` block or the same package `os` to check the presence of the file. What logic was used to decide that method `read_point_cloud` does not throw an error?