Fix loaders.cache patching

[pbs3141]

Follow-up to comment https://github.com/probonopd/go-appimage/issues/284#issuecomment-2205119529 in PR form.

This change results in the following output when patching loaders.cache:

Patching appdir/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache removing /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders/

I've verified that correctly patches loaders.cache, as confirmed by using it to build Inkscape (https://gitlab.com/pbs3141/inkscape/-/jobs/7264527507).

Fixes https://github.com/probonopd/go-appimage/issues/284

[probonopd]

Thank you very much @pbs3141