Fix AbstractLinkedList addAll returning true for an empty collection

[rootvector2]

addAll(int, Collection) hard-codes return true, so adding an empty collection reports a change that never happened, breaking the List.addAll contract (return true only if the list changed). Spotted because the class's own LinkedSubList.addAll already returns false for an empty collection, as does TreeList.addAll. The fix returns false for an empty collection after the getNode range check, so an out-of-range index still throws IndexOutOfBoundsException. AbstractLinkedListJava21 is a copy of this class with the same defect and gets the same one-line fix. Regression test in AbstractListTest runs against every list impl; it fails before for CursorableLinkedList, NodeCachingLinkedList and the AbstractLinkedListJava21 default list, and passes after.

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[garydgregory]

@rootvector2 Thank you for the PR, reviewed and merged 🚀