cache the bitmap converted to flat RGBA pixels.

Conflicts:
	chart2/source/view/inc/3DChartObjects.hxx
	chart2/source/view/main/3DChartObjects.cxx

Change-Id: Ied38d4457fbc04ded42fe4fb55a8ec654cefa259
prevent that early return prevents further user interaction

Change-Id: I24f814a402d2b8af3ddf888719b78d3158c2a38f