red-qxl: remove cookie assertion on scanout

The original check ensures we do not have an outstanding GL_DRAW. However,
in QEMU, there is no guarantee that a scanout cannot happen while the async
GL_DRAW has not returned a result yet. This introduces a race where if a
scanout is called while there is an outstanding GL_DRAW, QEMU will crash.

Signed-off-by: osy <osy@turing.llc>
Acked-by: Frediano Ziglio <freddy77@gmail.com>

server/red-qxl.cpp

@@ -432,7 +432,6 @@ void spice_qxl_gl_scanout(QXLInstance *qxl,
     spice_return_if_fail(qxl != nullptr);
 
     QXLState *qxl_state = qxl->st;
-    spice_return_if_fail(qxl_state->gl_draw_cookie == GL_DRAW_COOKIE_INVALID);
 
     pthread_mutex_lock(&qxl_state->scanout_mutex);