fdo#86708 paint after Undo of Sort

Regression of 10fc138307afb4b39baddb0d56eb8e986e5d29ea that exchanged
the PostPaint with SetDirty, but the paint is also needed.

Change-Id: Ic3e81fa106f405568effaed71ab33b575b4c5c5c
(cherry picked from commit 5cec4ea827570a5bb0a368025f3733b841107d07)