protected int findPreviousValidIndex(JPopupMenu popup, int startIndex) {

		for (int i = startIndex; i >= 0; i--) {
			Component c = popup.getComponent(i);
			if (isValidItem(c)) {
				return i;
			}
		}

		return -1;
	}
The work method of this handler.  This method will only be called when a menu or popup
menu is open.

@param manager the active menu selection manager
@param path the active menu path
Ghidra/Framework/Docking/src/main/java/docking/menu/keys/MenuKeyHandler.java