FIX: Markdown javascript error with certain formatting.

vendor/assets/javascripts/better_markdown.js

@@ -1011,6 +1011,7 @@
               var contents = this.processBlock(li_accumulate, []),
                   firstBlock = contents[0];
 
+              if (firstBlock) {
                 firstBlock.shift();
                 contents.splice.apply(contents, [0, 1].concat(firstBlock));
                 add( last_li, loose, contents, nl );
@@ -1024,6 +1025,7 @@
                 loose = false;
                 li_accumulate = "";
               }
+            }
 
             // Look at the next block - we might have a loose list. Or an extra
             // paragraph for the current li