Ctrl + +/- changes point size, not line width

[m3ht]

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Checklist

• [X] I have searched for similar issues.
• [X] For Python issues, I have tested with the latest development wheel.
• [X] I have checked the release documentation and the latest documentation (for master branch).

Describe the issue

Ctrl + +/- changes point size, not line width

Ubuntu 20.04, Open3d 0.15.2

Steps to reproduce the bug

# Render a line set using o3d.geometry.LineSet and open3d.visualization.draw_geometries

Error message

No response

Expected behavior

No response

Open3D, Python and System information

- Operating system: Ubuntu 20.04
- Python version: Python 3.8
- Open3D version: 0.15.2
- System architecture: x86 
- Is this a remote workstation?: no
- How did you install Open3D?: pip

Additional information

No response