Auto adjust scroll position after a sidebar is opened

[beru]

There's a case that selected node is hidden under a just opened sidebar.

Let me explaint this further. When a node is selected,

• Scroll position of the view is automatically adjusted.
• NODE PROPERTIES sidebar will be opened when it hasn't been shown yet.

And it looks like the auto adjustment of scroll position is carried out before the sidebar is opened. This causes the problem when the following conditions are met.

• The sidebar still hasn't been shown when a node is selected.
• A selected node is located on right side of the graph view.

Users can manually scroll the view to see the selected node after the sidebar is shown. But I just thought (the improvement of) automatic scrolling would be helpful.

[lutzroeder]

@beru can you investigate and submit a pull request.