You are given an array strarr of strings and an integer k. Your task is to return the first longest string consisting of k consecutive strings taken in the array.
#Example: longest_consec(["zone", "abigail", "theta", "form", "libe", "zas", "theta", "abigail"], 2) --> "abigailtheta"
n being the length of the string array, if n = 0 or k > n or k <= 0 return "".