Fix two consecutive newlines in nested lists

lib/lexer_block/list.js

@@ -193,10 +193,11 @@ module.exports = function list(state, startLine, endLine, silent) {
     if (nextLine >= endLine) { break; }
 
     if (isEmpty(state, nextLine)) {
-      nextLine++;
       if (nextLine >= endLine || isEmpty(state, nextLine)) {
         // two newlines end the list
         break;
+      } else {
+        nextLine++;
       }
     }