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