Given an array of integers $arr, return the sum of all the integers that have an even index, multiplied by the integer at the last index.
If the sequence is empty, you should return 0.
evenLast([2, 3, 4, 5]) ➞ 30
// numbers at even index = 2, 4
// number at last index = 5
// 2*5 + 4*5 = 10 + 20 = 30
evenLast([1, 3, 3, 1, 10]) ➞ 14
evenLast([]) ➞ 0N/A