cg: Fix use-after-free in put_ctls

Since we're freeing list entries don't forget to
initialize list then, otherwise it gets out with
free entries and may hit use-after-free bug.
Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/proc_parse.c

@@ -2302,6 +2302,7 @@ void put_ctls(struct list_head *l)
 		xfree(c->path);
 		xfree(c);
 	}
+	INIT_LIST_HEAD(l);
 }
 
 /* Parse and create all the real controllers. This does not include things with