 Failed to initialize NVML driver. If gpu is disabled 

I have a dedicated nvidia gpu on my laptop that I enable and disable. `nvidia` (proprietary) driver is loaded and unloaded accordingly

My thinkfan.conf
has section
``` 
sensors:
  - nvml: 03:00.0
    optional: true
```

but when gpu is off and nvidia driver is offloaded, I get
```
ERROR: Failed to initialize NVML driver. Error code (cf. nvml.h): 28
```
on thinkfan start