DDMarlinCED: layer count is also incremented for not drawn detector parts

[Zehvogel]

Like the title says. For passive (sub-)detectors (beampipe, supports, cables, etc.) the layer count is also incremented for detectors that are not set to be visible and thus not drawn (if surfaces are off or they have no surface). I.e. they use up a layer slot in the respective menu to toggle detector parts on or off in CED and those slots are very limited. The same can also happen for calorimeters and trackers but they are usually set to be visible anyway.

MarlinUtil/source/src/DDMarlinCED.cc

Lines 636 to 639 in f132e61

	getVisAttributes(det, color, visible);
	int layer = detLayer++;
	bool isDrawn = _surfaces && DrawSurfaces(surfMan, detName, color, layer);
	if (!isDrawn && visible){