Installing this on Hogfather causes HTTP 500 errors

[Alexander01998]

Log file with the exact error: error.log

Steps to reproduce

1. Open the Extension Manager.
2. Choose "manual install".
3. Try to install "html5video".
4. The entire wiki instantly stops working. Trying to access any page shows an HTTP 500 error.

System details

• DokuWiki 2020-07-29 "Hogfather"
• Ubuntu 20.04

[Klap-in]

These errors can be fixed with pull request: #10

@Fweeb do you have time to have a look at that pull request, and could you merge it please?