virLockSpacePreExecRestart: Avoid use-after-free

Recent refactor marked 'object' which is returned from the function as
autofree but forgot to use g_steal_pointer in the return statement to
prevent freeing it.

Fixes: 9a1651f64d
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/util/virlockspace.c

@@ -472,7 +472,7 @@ virJSONValuePtr virLockSpacePreExecRestart(virLockSpacePtr lockspace)
         goto error;
 
     virMutexUnlock(&lockspace->lock);
-    return object;
+    return g_steal_pointer(&object);
 
  error:
     virMutexUnlock(&lockspace->lock);