virtio-gpu: fix a missing check to avoid NULL dereference
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.15.61 by commit 39caef09666c1d8274abf9472c72bcac236dc5fb, it was introduced in version v4.4 by commit 62fb7a5e10962ac6ae2a2d2dbd3aedcb2a3e3257. For more details please see the references link.