Initialize maps during nvproxy restore.

The nvproxy restore code was not properly initializing the objsFreeSet map.
This caused a panic when this map was used after restore.

Fixes 1e1334e88f ("nvproxy: track driver object dependencies")

PiperOrigin-RevId: 627766876

pkg/sentry/devices/nvproxy/save_restore.go

@@ -34,4 +34,5 @@ func (n *nvproxy) afterLoad(goContext.Context) {
 		panic(fmt.Sprintf("driver version %q not found in abis map", n.version))
 	}
 	n.abi = abiCons.cons()
+	n.objsFreeSet = make(map[*object]struct{})
 }