gtk with virtio and opengl black screen
Description of problem:
Running the provided command line, the screen is black, and the vm still starts.
I can confirm that turning off gl (with gl=off), everything works.

These are line outputs printed out by QEMU:
```
gl_version 45 - core profile enabled
vrend_renderer_fill_caps: Entering with stale GL error: 1280
GLSL feature level 430
virtio_input_hid_handle_status: unknown type 20
virtio_input_hid_handle_status: unknown type 20
```
Steps to reproduce:
1. Execute the provided command
2. Wait
Additional information:
The bug was opened on launchpad by Ethan (ethannij). However, after the migration to github issues, the bug expired and no one reported here. This is the full launchpad discussion: https://bugs.launchpad.net/qemu/+bug/1898490