Fix max contrast retrieval to limit minimum color for relative time

[MorrisJobke]

Fixes regression from #14776.

maxContrastHex was #989898 in my case. The variables.css looked fine:

:root {
  --color-main-text: #222;
  --color-main-background: #fff;
  --color-main-background-translucent: rgba(255, 255, 255, 0.97);
  --color-background-dark: #ededed;
  --color-background-darker: #dbdbdb;
  --color-primary: #0082c9;
  --color-primary-text: #fff;
  --color-primary-text-dark: #ededed;
  --color-primary-element: #0082c9;
  --color-primary-element-light: #17adff;
  --color-error: #e9322d;
  --color-warning: #eca700;
  --color-success: #46ba61;
  --color-text-maxcontrast: #989898;
  --color-text-light: #484848;
...

Thus I trimmed the whitespace and now the file list does properly take it into account.

To test this you need quite old files to reach the limit. I changed the mtime entry to a timestamp of "1 year ago" in the file cache for the welcome.txt to trigger it.

cc @Charburner - #14776 (comment)

[MorrisJobke]

/backport to stable16

[skjnldsv]

Weird! 🤔

[MorrisJobke]

I pushed another fix. In IE 11 the getPropertyValue('--color-text-maxcontrast') returned nothing. The list of computed properties was filled, but was missing the custom properties. Thus I needed to trigger the fallback.

[backportbot-nextcloud]

backport to stable16 in #16543