Kitty shows error instead of image alt when file not found

I use kitty to view images and it often works.
```
inline_img_protocol 4
imgdisplay kitty
```

But for an image that has broken url, the output is
```
sh: line 1: /usr/lib/w3m/kitty: No such file or directory
```
In this case, I expect the alt text to be displayed.