fix: comments check (fix #931)

Author: yyx990803

lib/loader.js

@@ -89,7 +89,7 @@ module.exports = function (content) {
   var output = ''
   var parts = parse(content, fileName, this.sourceMap)
   var hasScoped = parts.styles.some(function (s) { return s.scoped })
-  var hasComment = parts.template && parts.template.attrs.comments
+  var hasComment = parts.template && parts.template.attrs && parts.template.attrs.comments
 
   var templateCompilerOptions = '?' + JSON.stringify({
     id: moduleId,