Function iter_merge_sort has bug where array with length 2 is not sorted

[dangbb]

Test Report - Iter merge sort function.pdf
Here all the report.

[dangbb]

Also, the main function has a bug where user can't enter empty input.
The following is the log:

Traceback (most recent call last):
  File "sorts\iterative_merge_sort.py", line 73, in <module>
    unsorted = [int(item.strip()) for item in user_input.split(",")]
  File "sorts\iterative_merge_sort.py", line 73, in <listcomp>
    unsorted = [int(item.strip()) for item in user_input.split(",")]
ValueError: invalid literal for int() with base 10: ''