Fix two bugs in findLast and findLastIndex

This fixes two issues:

(1) If only the first element of an array matched the predicate, neither findLast nor findLastIndex
would report is as present.

(2) More critically, if queried with an empty array, both functions would enter into an infinite
loop.
Merge pull request #333 from markprzepiora/fix-find-last-bugs

Fix two bugs in findLast and findLastIndex