CSS files downloaded only after reloading page

Hi Dillo developers,

the dillo version from the repository seems to have problems
downloading some CSS files the first time some pages are loaded.
Though, the remaining CSS files are downloaded when the page is
re-loaded using CTRL-r.

Example page:

  https://netzpolitik.org/

Reproduce:

  1) dillo https://netzpolitik.org/
     -> styles from some CSS files seem to be missing
  2) press CTRL-r
     -> some new CSS file is downloaded and styles are applied
  3) press CTRL-r
     -> some new CSS file is downloaded and styles are applied

Best regards,
Alex