wlr_xwayland_server_destroy gets called by itself, resulting in a double free

This is for version 0.15.1, I haven't seen anything to fix this after...

Steps to reproduce:

1. Ensure an xwayland server is created via wlr_xwayland_create
2. Destroy the xwayland server using wl_display_destroy

The wlr_xwayland_server_destroy function is indirectly called by itself through this function chain:

1. wlr_xwayland_server_destroy
2. wlr_xwayland_destroy
3. handle_server_destroy
4. wlr_signal_emit_safe
5. wlr_xwayland_server_destroy

I'm not sure how to fix this because each individual function calling the others looks fine, but together they form a loop. Should the xwayland server not emit the destroy event? Should the handle_server_destroy not call wlr_xwayland_destroy? None seem like good options...