Inpainting error: `TypeError: unsupported operand type(s) for -: 'list' and 'int'`

For some reason, I keep getting this bizarre error that occurs whenever I try to inpaint. I'm not trying to use any scripts, although it doesn't matter if I specify a script or not - something is expecting an integer and getting a list, and I suspect it is because `script_index` is an incorrect value: `self.selectable_scripts[script_index-1]`.

```
Error completing request
Arguments: ('', 4, 'asdf', 'asdf', 'None', , None, None, None, None, , , 150, 17, 0, None, 1, False, False, 1, 1, 5.0, 0, 0.75, -1, -1, 0.0, 0, 0, False, 512, 512, 1, False, 0, False, '', '', '', [], 0) {}
Traceback (most recent call last):
File "A:\Programs\stable-diffusion-webui\modules\call_queue.py", line 56, in f
res = list(func(*args, **kwargs))
File "A:\Programs\stable-diffusion-webui\modules\call_queue.py", line 37, in f
res = func(*args, **kwargs)
File "A:\Programs\stable-diffusion-webui\modules\img2img.py", line 166, in img2img
processed = modules.scripts.scripts_img2img.run(p, *args)
File "A:\Programs\stable-diffusion-webui\modules\scripts.py", line 370, in run
script = self.selectable_scripts[script_index-1]
TypeError: unsupported operand type(s) for -: 'list' and 'int'
```

The effect is that the selected layer has its visibility toggled off, and nothing else happens.