Issue 7229 - Fixed: Whitelisted websites list not sorted alphabetically

This MR is for #240 (closed). When initializing custom filters, the acceptableAdsUrl and acceptableAdsPrivacyUrl variables haven't been set yet and are therefore null. That means that calling isAcceptableAdsUrl(filter.url) returns true because filter.url is undefined and no sorting occurs.

Alternatively, I could've changed == to === but that would still not be sufficient as isAcceptableAdsUrl(null) shouldn't return true.

I understand that this fix doesn't resolve the underlying issue (i.e. ensure that variables have been set before using them) but changing isAcceptableAdsUrl() to return a promise and other related changes would require quite a bit of rewriting.