Opening dashboard breaks Nvim's alternate file

[Riyyi]

Describe the bug
When navigating between files, I use the alternate file feature via <C-6>. If I switch to the dashboard via the :Dashboard command, I think an empty string is inserted into the alternate file, and I can't navigate back anymore.

To Reproduce
Steps to reproduce the behavior:

1. Open Neovim
2. Open a project file
3. Open a second project file
4. Run :Dashboard
5. Press <C-6>, it returns to the second project file
6. Press <C-6> again
7. See error: E23: No alternate file

My configuration:

	-- Dashboard
	{
		"nvimdev/dashboard-nvim",
		event = "VimEnter",
	},

Expected behavior
I find either behavior acceptable

• Opening the dashboard creates a normal buffer, so after step 6 it returns to the dashboard buffer
• Opening the dashboard doesn't pollute the alternate file, so after step 6 it returns to the first project file