BUG: r21160 fixed crosshairs but broke 3D viewer. r21165 fixed 3D viewer but brok crosshairs. This patch fixes both.

Moved the code introduced in r21165 down a few lines.

If the interactor is cached earlier, then the events registered in
AdditionalInitializationStep() don't get observed (which the Crosshairs depend
on).

I don't understand why moving the lines fixes the issue. In both r21165 and
in this patch, the events added in AdditionalInitializeStep() are only cached
locally and are not actually assigned to the interactor at that time.

But there must be some observer side effect that by observing the interactor,
another event is triggered, which causes the events/observers to be lost.
Perhaps another interactor gets puts in place? Or not in place?

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21186 3bd1e089-480b-0410-8dfb-8563597acbee