CVE-2022-49532 drm/virtio: fix NULL pointer dereference in virtio_gpu_conn_get_modes

In the Linux kernel, the following vulnerability has been resolved: drm/virtio: fix NULL pointer dereference in virtiogpuconngetmodes drmcvtmode may return NULL and we should check it. This bug is found by syzkaller: FAULTINJECTION stacktrace: 168.567394 FAULTINJECTION: forcing a failure. name...