Don't crash when eglCreateContext fails

eglCreateContext fails with every EGLConfig that
nvidia blob 334.16 provides causing NULL pointer
dereference in gl_renderer_destroy when destroying
fragment and fan bindings.

https://bugs.freedesktop.org/show_bug.cgi?id=74699

Signed-off-by: Mariusz Ceier <mceier+wayland@gmail.com>

src/gl-renderer.c

@@ -1766,7 +1766,9 @@ gl_renderer_destroy(struct weston_compositor *ec)
 	wl_array_release(&gr->vertices);
 	wl_array_release(&gr->vtxcnt);
 
+	if (gr->fragment_binding)
 		weston_binding_destroy(gr->fragment_binding);
+	if (gr->fan_binding)
 		weston_binding_destroy(gr->fan_binding);
 
 	free(gr);