ParseResponseForCert would previously complain about an invalid hash OID if the response contained no SingleResponse matching the certificate provided by the caller. Fixes golang/go#19540 Change-Id: I0354c4048707a788ed3d184cc88b4f13f65544ba Reviewed-on: https://go-review.googlesource.com/44005 Reviewed-by: Adam Langley <agl@golang.org>