--allow-local-files may not be accepted local files depending on the environment

[yhatt]

It was reported in marp-team/marp-vscode#64. (marp-team/marp-vscode#64 (comment))

We cannot yet identify this cause. The following is a list of concerns that might be possible to be a cause.

• The base URI of converting file specified by <base> HTML element would have wrong encoding
• Something cannot parse special characters like spaces, parentheses, and so on (Similar to Marp CLI cannot find a file that name has a pair of brackets #95)
• Marp CLI may fail handling on-demand files (DropBox, OneDrive, Google Drive etc)

[yhatt]

In a situation of marp-team/marp-vscode#64, we found that <base> file URL has use incorrect path while exporting PDF.

<base href="file://C:\Users\xxxxx\AppData\Local\Programs\Microsoft VS Code/c:\Users\xxxxx\Dropbox (uscitp)\_ITP 348\_Content (public)\_lectures\_week3\filename.md">