LSM: SafeSetID: Stop releasing uninitialized ruleset

The first time a rule set is configured for SafeSetID, we shouldn't be
trying to release the previously configured ruleset, since there isn't
one. Currently, the pointer that would point to a previously configured
ruleset is uninitialized on first rule set configuration, leading to a
crash when we try to call release_ruleset with that pointer.
Acked-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>

security/safesetid/securityfs.c

@@ -187,7 +187,8 @@ static ssize_t handle_policy_update(struct file *file,
 out_free_buf:
 	kfree(buf);
 out_free_pol:
-	release_ruleset(pol);
+	if (pol)
+                release_ruleset(pol);
 	return err;
 }