Score player handle

A party game scores player handles: each letter is worth its position in the alphabet ('a' or 'A' is 1, 'b' is 2, ..., 'z' is 26), and every other character is worth nothing. Given a handle, return its total score. For example, 'abz' scores 1 + 2 + 26 = 29, and 'cab_7' scores 3 + 1 + 2 = 6.