crypto/tls: fix clientHelloMsg fuzzer not to generate the RI SCSV
crypto/tls: fix clientHelloMsg fuzzer not to generate the RI SCSV

It was causing mysterious fuzzing failure because it affects the
unmarshaling of the secureNegotiationSupported field.

Change-Id: Id396b84eab90a3b22fb6e306b10bdd7e39707012
Reviewed-on: https://go-review.googlesource.com/60912
Run-TryBot: Filippo Valsorda <c22b5f9178342609428d6f51b2c5af4c0bde6a42@filippo.io>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

akutz/go,golang/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,polyverse-security/go,cloudflare/go,nawawi/go,codestation/go,codestation/go,josharian/go,nawawi/go,akutz/go,golang/go,cloudflare/go,codestation/go,CAFxX/go,CAFxX/go,nawawi/go,josharian/go,Cofyc/go,akutz/go,Cofyc/go,codestation/go,golang/go,codestation/go,Cofyc/go,polyverse-security/go,cloudflare/go,josharian/go,polyverse-security/go,cloudflare/go,josharian/go,golang/go,Cofyc/go,akutz/go,polyverse-security/go,nawawi/go,josharian/go,cloudflare/go,akutz/go,codestation/go,nawawi/go,CAFxX/go,Cofyc/go,cloudflare/go,codestation/go,Cofyc/go,polyverse-security/go,josharian/go,golang/go,CAFxX/go,josharian/go,christopher-henderson/Go,codestation/go,golang/go,polyverse-security/go,Cofyc/go,polyverse-security/go,akutz/go,CAFxX/go,CAFxX/go,nawawi/go,akutz/go,golang/go,nawawi/go,polyverse-security/go,cloudflare/go,akutz/go,cloudflare/go,Cofyc/go,josharian/go