nvim +"Man man" not work as expected
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## Expected behavior, english is required

``neovim`` has an internal command ``Man``, which show manpage inside vim.
When we start nvim with ``nvim +"Man man"``, it should display a single window with the manpage of ``man`` command.
But it shows the welcome page.  Pressing ``[SPC]<tab>`` will show the manpage in the upper window.

## The reproduce ways from Vim starting (Required!)

1. Execute the command
   ```sh
   nvim +"Man man"
   ```
2. Press ``[SPC]<tab>``

## Output of the `:SPDebugInfo!`

## Screenshots

If you have any screenshots for this issue, please upload here. BTW you can use https://asciinema.org/ for recording video in terminal.

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