After activating or deactivating fullscreen mode, the sidebar
window is automatically moved to its start, while scroll bar
stays in its original position.

The sidebar window move is unwanted and unsolicited, and it's
most probably caused by GtkIconView or GtkScrolledWindow bug.

Workaround this by having the sidebar sync its window with the
current scroll position after a fullscreen operation, do that by
just emitting a "value-changed" on the current scroll adjustment.

https://bugzilla.gnome.org/show_bug.cgi?id=783404