fixes #7;Chapter04 - implementation of 'append_at_a_location'

[amirsoroush]

Hi, Current implementation needs two small changes to work correctly:

1. The first if statement should be if index == 1: otherwise count is already 1 and it prevents the rest of the code to run.
2. In elif part, index == index always evaluates to True. This also should be elif count == index.

I also changed if count <= index: so that if index is 4 it says that "The list has less number of elements" otherwise it silently skips the append and says nothing.