Voronoi Diagram fails with Bounding box: Automatic from selected objects
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#### Steps to reproduce:
<!-- Describe what you did (step-by-step) so we can reproduce: -->
- open Inkscape
- create few circles or rectangles on layer 2
- select all and go to extensions - > Generate from path - > voronoi diagram
- Make sure Type: Voronoi OR Voronoi and Delaunay
- Make sure Bounding box: Automatic from selected objects
- Apply
#### What happened?
Voronoi diagram failed to work.
```
Traceback (most recent call last):
File "voronoi2svg.py", line 292, in <module>
Voronoi().run()
File "C:\APP\Temp\inkscape_devel\share\inkscape\extensions\inkex\base.py", line 140, in run
self.save_raw(self.effect())
File "voronoi2svg.py", line 222, in effect
clip_box = (2 * group_bbox[0] - group_bbox[1],
TypeError: 'BoundingBox' object is not subscriptable
```
#### What should have happened?
Voronoi diagram should work.
#### Inkscape Version and Operating System:
- Inkscape Version: 1.0 <!-- (run inkscape -V or copy from Help → About Inkscape, top right) -->
- Operating System: Debian 10 buster.
- Operating System version: 10
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issue