lazygit fails to open on first launch due to the assumption that config.yml exists

Currently, the lazygit module assumes `config.yml` exists in its default location when it sets `$LG_CONFIG_FILE`, but that file doesn't get created until first launch, and if the aforementioned variable contains a file that doesn't exist, it fails to launch.
```
$ lazygit             
2025/01/10 20:31:53 stat /home/shaun/.config/lazygit/config.yml: no such file or directory
```