go.net/html: Fix comment handling for "in select" insertion mode
go.net/html: Fix comment handling for "in select" insertion mode

LGTM=andybalholm, nigeltao
R=golang-codereviews, gobot, nigeltao, andybalholm
CC=golang-codereviews
https://golang.org/cl/93680045

dafyddcrosby/net,cmars/tools,zabawaba99/net,cesanta/goxnet,kiip/net,w4ngyi/net,muzining/net,cesanta/goxnet,raboof/net,DramaFever/golang.org-x-net,golang/net,yangxianjun/net,mckinney-subgraph/net,albertjin/golang-net,cmars/tools,w4ngyi/net,gomini/net,gomini/net,chenzlabs/net,raboof/net,foreversmart/net,chenzlabs/net,mckinney-subgraph/net,subuk/net,flowlo/go-net,cmars/tools,veliamsli/net,muzining/net,DramaFever/golang.org-x-net,flowlo/go-net,veliamsli/net,foreversmart/net,dafyddcrosby/net,cmars/tools,zabawaba99/net,albertjin/golang-net,kiip/net,yangxianjun/net,subuk/net