To avoid leaking memory on the error path, reorder the
code as:
- check the parameters first
- check resource already existing
- finally allocate memory

Reported-by: Coverity (CID 1453811: RESOURCE_LEAK)
Fixes: e0933d91 ("virtio-gpu: Add virtio_gpu_resource_create_blob")
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210531101928.1662732-1-philmd@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>