i#124999: - call <SwGrfNode::onGraphicChanged()> only when <Graphic>

instance has been set, too

- <SwGrfNode::onGraphicChanged()> - assure that graphic is swapped
  out in case its swap in has been triggered by this method.

(cherry-picked from commit 4dbdc0ce931d7686583a49e68f8df09827357beb)

Change-Id: I3e6aa68d9507095925dec37075abcdf9da58c804
revert sw part of "don't swap in all images when loading files"

Half of commit 9b9eb2e4f619c63eabdc54b5d749ac55d8eaf333 is obsoleted
by orw's fix for i#124999; not sure about the other half.

Change-Id: I337a4bbf79912c02be7c7c56c5705253b3d7b125