Given a list and an integer n, return the sum of the first n numbers in the list.
sum_first_n_nums([9, 8, 7, 6], 3) ➞ 24
# The parameter n is specified as 3.
# The first 3 numbers in the list are 9, 8 and 7.
# The sum of these 3 numbers is 24 (9 + 8 + 7).
# Return the answer.
sum_first_n_nums([1, 3, 2], 2) ➞ 4
sum_first_n_nums([4, 2, 5, 7], 4) ➞ 18
sum_first_n_nums([3, 6, 2], 0) ➞ 0
If n is larger than the length of the list, return the sum of the whole list.