text: Title: Cannot append elements to shell array while using tqdm
  Body: - [ ] I have marked all applicable categories:
      + [ ] exception-raising bug
      + [ ] visual output bug
      + [x] Command-line unintentional behaviour
  - [x] I have visited the [source website], and in particular
    read the [known issues]
  - [x] I have searched through the [issue tracker] for duplicates
  - [x] I have mentioned version numbers, operating system and
    environment, where applicable:
    ```bash
    python -c "import tqdm, sys; print(tqdm.__version__, sys.version, sys.platform)"
     4.60.0 3.8.0 (default, Oct  6 2020, 11:07:52) 
     [GCC 10.2.0] linux
    ```
  
  [source website]: https://github.com/tqdm/tqdm/
  [known issues]: https://github.com/tqdm/tqdm/#faq-and-known-issues
  [issue tracker]: https://github.com/tqdm/tqdm/issues?q=
  
  I have encountered an issue where elements are not appended to shell arrays when using the tqdm bar from the terminal. The following example produces an empty array
  ```
  $ test_arr=()
  total=10
  for i in $(seq $total)
  do
      echo "$i"
      test_arr+=("$i")
  done | tqdm --total $total --null
  echo "Size of array: ${#test_arr[@]}"
  echo "with elements: ${test_arr[@]}"
  100%|████████████████████████████████████████████████████████████████████████████| 10/10 [00:00<00:00, 242445.32it/s]
  Size of array: 0
  with elements:
  ```
  
  Whereas the elements are properly added if you remove the bar
  ```
  $ test_arr=()
  total=10
  for i in $(seq $total)
  do
      echo "$i"
      test_arr+=("$i")
  done
  echo "Size of array: ${#test_arr[@]}"
  echo "with elements: ${test_arr[@]}"
  1
  2
  3
  4
  5
  6
  7
  8
  9
  10
  Size of array: 10
  with elements: 1 2 3 4 5 6 7 8 9 10
  ```