platform: do not pass a directory on the command line.
The home directory will be properly set by Device.home_dir.
It was sometimes crashing when opened with no args.
Fixes: #7049
Update shellcheck and shfmt to the latest version.
Fixes <https://github.com/koreader/koreader/issues/5152>.
Btw, you can apply shellcheck suggestions with a command like:
```
shellcheck --include=SC2250 -f diff *.sh | git apply
```
