Setting XDG_CACHE_HOME and/or XDG_DATA_HOME breaks application

[JoelleJS]

Describe the bug
These are two bugs with setting XDG environment variables:

• Setting XDG_CACHE_HOME makes the application look for nwg-dock-pinned in the $HOME/.config dir:

ERRO[0000] Unable to show grid button: open /home/yourusername/.config/nwg-dock-pinned: no such file or directory

• Setting XDG_DATA_HOME to anything else than /usr/share makes the application look for the application images in $XDG_DATA_HOME/nwg-dock-hyprland/images instead of /usr/share/nwg-dock-hyprland/images, resulting in a panic:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x5e3243]

To Reproduce
Steps to reproduce the behavior:

1. Start the application with either environment variable set

Expected behavior

• The application looks for nwg-dock-pinned in $XDG_CACHE_HOME
• The application looks for its images in /usr/share/nwg-dock-hyprland/images

Desktop (please complete the following information):

• Linux distribution: Arch Linux
• go version: go1.22.3 linux/amd64
• gtk-layer-shell version: 0.8.2-1

[nwg-piotr]

@JoelleJS before I release, I'd like to wait for @dlasky to merge dlasky/gotk3-layershell#8, and then merge #37.

[dlasky]

needs some work to build but its close

[nwg-piotr]

@dlasky Thanks!