[markdown mode] Always make a blank line terminate an HTML block
[markdown mode] Always make a blank line terminate an HTML block

As per http://spec.commonmark.org/0.27/#html-blocks

Issue #4611

wingify/CodeMirror,dperetti/CodeMirror,jayaprabhakar/CodeMirror,mtaran-google/CodeMirror,namin/CodeMirror,grzegorzmazur/CodeMirror,ficristo/CodeMirror,MarcelGerber/CodeMirror,thomasjm/CodeMirror,thomasjm/CodeMirror,ficristo/CodeMirror,pabloferz/CodeMirror,codio/CodeMirror,wingify/CodeMirror,nightwing/CodeMirror,crazy4chrissi/CodeMirror,kerabromsmu/CodeMirror,kerabromsmu/CodeMirror,mtaran-google/CodeMirror,hackmdio/CodeMirror,namin/CodeMirror,ejgallego/CodeMirror,nightwing/CodeMirror,grzegorzmazur/CodeMirror,dperetti/CodeMirror,notepadqq/CodeMirror,namin/CodeMirror,kerabromsmu/CodeMirror,codio/CodeMirror,grzegorzmazur/CodeMirror,dperetti/CodeMirror,ejgallego/CodeMirror,crazy4chrissi/CodeMirror,SidPresse/CodeMirror,schanzer/CodeMirror,schanzer/CodeMirror,MarcelGerber/CodeMirror,wingify/CodeMirror,pabloferz/CodeMirror,jayaprabhakar/CodeMirror,hackmdio/CodeMirror,mtaran-google/CodeMirror,ficristo/CodeMirror,pabloferz/CodeMirror,SidPresse/CodeMirror,hackmdio/CodeMirror,nightwing/CodeMirror,jkaplon/CodeMirror,jkaplon/CodeMirror,jkaplon/CodeMirror,crazy4chrissi/CodeMirror,ejgallego/CodeMirror,jayaprabhakar/CodeMirror,SidPresse/CodeMirror,notepadqq/CodeMirror,codio/CodeMirror,MarcelGerber/CodeMirror,notepadqq/CodeMirror,thomasjm/CodeMirror,schanzer/CodeMirror