"get_image" of LayoutView should also work on inactive views

[klayoutmatthias]

See https://www.klayout.de/forum/discussion/2365/problem-with-saving-screenshots-while-changing-layers-groups-visibility#latest for ongoing discussion.

Technically the reason for the problem is that LayoutViewBase::refresh down in the call chain sometimes skips set_view_ops if the view is not active. But calling "update_content" in that case should fix the problem as a workaround.