Kill a subwindow if it exists

// KillChildWindowIfItExists(windowName, childWindowName)
// Kills a child window of a top-level window if it exists or does nothing if the child does not exist.
// Returns 0 if it killed the child window, -1 if not.
// If you pass "" for windowName it uses the target window.
Function KillChildWindowIfItExists(windowName, childWindowName)
	String windowName				// Name of a top-level window or "" for top target window
	String childWindowName			// Name of child window
	
	if (strlen(windowName) == 0)
		Variable mask = -1 & ~128			// All window types except for procedure windows
		windowName = WinName(0, -1)
	endif
	
	String list = ChildWindowList(windowName)
	if (WhichListItem(childWindowName,list) < 0)
		return -1
	endif
	
	String path = windowName + "#" + childWindowName
	KillWindow $path
	return 0
End