Fix improperly unselecting imported lists

Related feedback:
- https://www.reddit.com/r/uBlockOrigin/comments/13enzvv/

When assessing which default lists to disable/enable after
updating from 1.48.x to 1.49.x, uBO has to ignore imported
lists, as these do not have a `off` property -- the
non-existence of this property was used to determine whether
a list was default or not. There needs to be an extra test for
whether the list is imported or not.

src/js/storage.js

@@ -1625,7 +1625,11 @@ self.addEventListener('hiddenSettingsChanged', ( ) => {
         if ( newDefaultListset.size === 0 ) { return; }
         if ( oldDefaultListset.size === 0 ) {
             Array.from(Object.entries(oldDict))
-                .filter(a => a[1].content === 'filters' && a[1].off === undefined)
+                .filter(a =>
+                    a[1].content === 'filters' &&
+                    a[1].off === undefined &&
+                    /^https?:\/\//.test(a[0]) === false
+                )
                 .map(a => a[0])
                 .forEach(a => oldDefaultListset.add(a));
             if ( oldDefaultListset.size === 0 ) { return; }