Fix compatibility issues from preloading images

[edrpls]

#31 introduced a possible problem when loading the module as CJS or ESM, since the browser version checks for DOM nodes to get the root URL where the script is loaded from.

[edrpls]

FYI, I now believe that said root URL validation is unnecessary. A user loading ggezvp more than once is probably a small edge-case we should not care about.