xwayland: Make resizing work again

xwayland: Make resizing work again

9c376b54ea6f60ae10d93653132e22ef66a536d7 fixed the crash when a client goes
away during a resize grab.  The shsurf->resource is set to NULL in that
case and we were trying to send out events to a NULL resource.  However,
xwayland shell surfaces are created by the xwayland module and don't have a
resource.  We use a different function pointer for sending the configure
events that handle the events inside xwayland instead of sending protocol
events.

To fix all this, we just move the check for a NULL resource into the
functions that we use for sending configure events for wl_shell and
xdg_shell.