CHUI-59 FIX Floater stacking offset only occurs first time a floater is opened

changed stacking logic to attempt to stack against any floater that is cascade head
*or* in a cascade group

indra/llui/llfloaterreg.cpp

@@ -96,7 +96,9 @@ LLFloater* LLFloaterReg::getLastFloaterCascading()
 		{
 			LLFloater* inst = *iter;
 
-			if (inst->getVisible() && inst->isPositioning(LLFloaterEnums::POSITIONING_CASCADING))
+			if (inst->getVisible() 
+				&& (inst->isPositioning(LLFloaterEnums::POSITIONING_CASCADING)
+					|| inst->isPositioning(LLFloaterEnums::POSITIONING_CASCADE_GROUP)))
 			{
 				if (candidate_rect.mTop > inst->getRect().mTop)
 				{