files: Fix colormode detection for filelist
files: Fix colormode detection for filelist

When system default color theme is selected for theming, the `enabledThemes` array
is empty or just contains on entry `'default'`, in this case the color theme has
to be retrieved from the browser to ensure text like the modified date is readable.

This fixes #33298

Signed-off-by: Ferdinand Thiessen <d839ee45896e6fd6af263edfd34014da50964f0b@fthiessen.de>

nextcloud/server,nextcloud/server,nextcloud/server,nextcloud/server