EXP-1840 FIXED (When two inventory windows are open and "properties" are...

EXP-1840 FIXED (When two inventory windows are open and "properties" are viewed, one window suddenly moves in front of the other window)

- Modified method LLFloaterSidePanelContainer::openChildPanel so that it doesn't open floater each time it's called. Otherwise each time opening child panel of already opened floater, openFloater() will reposition the floater.