[Bug] : count property of `columns` shortand gets removed

**Describe the bug**

A clear and concise description of what the bug is.

`columns: 2 200px` gets transformed into `columns: 200px`, removing the 'count' property.

`columns: 200px 2` produces the same result.



**To Reproduce**

Steps to reproduce the behavior:

<!-- **Please add a reproducible repo or sandbox** -->

1. Run cssnano over the above CSS.



**Expected behavior**

A clear and concise description of what you expected to happen.

I'd expect the count property to be preserved in the value.



**Screenshots**

If applicable, add screenshots to help explain your problem. (from [cssnano-playground](https://cssnano.co/playground/))



**Desktop (please complete the following information):**

- CSSNANO Version 5.0.3

- preset: 'default'

- Add the output of `npx envinfo && npm ls cssnano` here

```

  System:

    OS: Linux 5.11 Ubuntu 21.04 (Hirsute Hippo)

    CPU: (12) x64 Intel(R) Core(TM) i7-10710U CPU @ 1.10GHz

    Memory: 8.02 GB / 31.20 GB

    Container: Yes

    Shell: 5.8 - /usr/bin/zsh

  Binaries:

    Node: 14.17.0 - ~/.nvm/versions/node/v14.17.0/bin/node

    npm: 7.13.0 - ~/.nvm/versions/node/v14.17.0/bin/npm

  Managers:

    Apt: 2.2.3 - /usr/bin/apt

    Composer: 2.0.13 - ~/.config/composer/composer

    pip3: 20.3.4 - /usr/bin/pip3

  Utilities:

    CMake: 3.20.2 - /snap/bin/cmake

    Make: 4.3 - /usr/bin/make

    GCC: 10.3.0 - /usr/bin/gcc

    Git: 2.30.2 - /usr/bin/git

    FFmpeg: 4.3.2 - /usr/bin/ffmpeg

  IDEs:

    Nano: 5.4 - /usr/bin/nano

    VSCode: 1.56.2 - /usr/bin/code

  Languages:

    Bash: 5.1.4 - /usr/bin/bash

    Perl: 5.32.1 - /usr/bin/perl

    PHP: 7.4.16 - /usr/bin/php

    Python3: 3.9.4 - /usr/bin/python3

  Browsers:

    Chrome: 90.0.4430.212

    Firefox: 88.0.1

```



**Additional context**

Add any other context about the problem here.

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