IGV: Zooming changes the point that is currently centered

Zooming can change the part of the graph that is currently centered but it should not.

Steps to reproduce:

* Open attachment zoom_bug.xml in IGV

* Open graph "After Parsing"

* Click on "Show satellite view of the whole graph" on the toolbar

* The grey rectangle shows the currently viewed part of the graph

* Move rectangle to top right

* Use the toolbar to zoom in (magnifying glass with a +)

* Rectangle disappears (also a bug)

* Zoom out (magnifying glass with a -)

* Rectangle reappears

* Zoom in (+)

* Rectangle jumps to the left. It should not change the part of the graph that is centered when zooming.