crypto/x509: don't ignore asn1.Marshal error
crypto/x509: don't ignore asn1.Marshal error

I don't see how the call could fail, so, no test. Just a code cleanup in
case it can fail in the future.

Fixes #15987.

Change-Id: If4af0d5e7d19cc8b13fb6a4f7661c37fb0015e83
Reviewed-on: https://go-review.googlesource.com/23860
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>

goodlang/good,codestation/go,golang/go,CAFxX/go,vsekhar/elastic-go,goodlang/good,Cofyc/go,nawawi/go,akutz/go,vsekhar/elastic-go,linux-on-ibm-z/go,akutz/go,Cofyc/go,codestation/go,theif519/go,ImJasonH/go,akutz/go,polyverse-security/go,Cofyc/go,derekmarcotte/go,derekmarcotte/go,vsekhar/elastic-go,vsekhar/elastic-go,suncycheng/go,theif519/go,ImJasonH/go,nawawi/go,momchil-velikov/go,ImJasonH/go,derekmarcotte/go,golang/go,vsekhar/elastic-go,golang/go,goodlang/good,nawawi/go,suncycheng/go,CAFxX/go,nawawi/go,ImJasonH/go,josharian/go,momchil-velikov/go,4ad/go,golang/go,momchil-velikov/go,suncycheng/go,polyverse-security/go,4ad/go,golang/go,linux-on-ibm-z/go,linux-on-ibm-z/go,polyverse-security/go,derekmarcotte/go,codestation/go,suncycheng/go,cloudflare/go,derekmarcotte/go,Cofyc/go,momchil-velikov/go,linux-on-ibm-z/go,linux-on-ibm-z/go,CAFxX/go,4ad/go,4ad/go,nawawi/go,akutz/go,josharian/go,CAFxX/go,vsekhar/elastic-go,vsekhar/elastic-go,cloudflare/go,theif519/go,theif519/go,josharian/go,ImJasonH/go,suncycheng/go,suncycheng/go,polyverse-security/go,goodlang/good,Cofyc/go,codestation/go,codestation/go,cloudflare/go,akutz/go,cloudflare/go,Cofyc/go,momchil-velikov/go,derekmarcotte/go,Cofyc/go,CAFxX/go,nawawi/go,cloudflare/go,goodlang/good,cloudflare/go,cloudflare/go,josharian/go,golang/go,josharian/go,linux-on-ibm-z/go,4ad/go,cloudflare/go,theif519/go,ImJasonH/go,linux-on-ibm-z/go,derekmarcotte/go,nawawi/go,derekmarcotte/go,ImJasonH/go,CAFxX/go,ImJasonH/go,goodlang/good,josharian/go,theif519/go,codestation/go,suncycheng/go,josharian/go,4ad/go,christopher-henderson/Go,polyverse-security/go,golang/go,codestation/go,theif519/go,4ad/go,CAFxX/go,linux-on-ibm-z/go,4ad/go,polyverse-security/go,momchil-velikov/go,goodlang/good,nawawi/go,akutz/go,momchil-velikov/go,momchil-velikov/go,akutz/go,vsekhar/elastic-go,polyverse-security/go,golang/go,Cofyc/go,goodlang/good,suncycheng/go,akutz/go,theif519/go,CAFxX/go,josharian/go,polyverse-security/go,codestation/go