Following up #856: when the keymap doesn't have the keysym we need... we just can't handle the key event. See also #1049
Solutions:
With the HTML5 client, we don't really have a list of keysyms pre-defined in advance: the client is free to use whatever input method is available to it, and we get unicode characters in the events.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2597