Shellcheck the script

* 🚨 shellcheck'ed with some suggestions from @yubiuser

* 🚨 shellcheck'ed with some more suggestions from @yubiuser

* undo the change in the sqlite query (mapfile) + keep the check mark

* Adapt some more real nice proposals from @yubiuser

* Fix: SC2178 (warning): Variable was used as an array but is now assigned a string.

adapt suggestion
Co-authored-by: yubiuser <ckoenig@posteo.de>

* Update pihole_adlist_tool

Co-authored-by: yubiuser <ckoenig@posteo.de>

* Update pihole_adlist_tool

Co-authored-by: yubiuser <ckoenig@posteo.de>

* Update pihole_adlist_tool

Co-authored-by: yubiuser <ckoenig@posteo.de>

* Update pihole_adlist_tool

Co-authored-by: yubiuser <ckoenig@posteo.de>

* Update pihole_adlist_tool

Co-authored-by: yubiuser <ckoenig@posteo.de>

* Fix: SC2145 (error): Argument mixes string and array. Use * or separate argument.

* Fix declaration of LEFT_DOMAINS

* Revert unneccessary shellcheck'ed lines

* Update pihole_adlist_tool

Co-authored-by: yubiuser <ckoenig@posteo.de>

Co-authored-by: yubiuser <ckoenig@posteo.de>