backend-wayland: fix error path in wayland_backend_create
Destroy the renderer before disconnecting the Wayland display. Trying to destroy the GL renderer with the Wayland display already gone crashes in the Mesa Wayland integration.
For this, the GL renderer needs to clear the compositor->renderer
pointer during gl_renderer_destroy()
so that weston_compositor_shutdown()
doesn't try to destroy the renderer again. The Pixman and no-op renderers already clear the pointer during destroy.