Sidebar scroll glitchy.

[hifall]

In some case, the sidebar doesn't expand to full page height, when browser height increases.

To repro:
1 open up the Chrome browser, resize it so that it's height is about half screen height, and it's width is about full screen width;
2 navigate to a Grav Learn2 theme page in the browser, for example: https://learn.getgrav.org/. The requirement here is that the sidebar should be long "enough" (about screen height), otherwise the issue won't manifest;
3 after the page is fully loaded, drag the bottom border of the browser to increase the page height;
4 the sidebar's height should grow; instead, it doesn't.