Merge pull request #54 from ridi/feature/v2-revise-images

reviseImages의 callback 유효할때만 호출하도록

Author: Kyungtae-TEI

src/common/_Content.js

@@ -488,7 +488,9 @@ class _Content {
    */
   reviseImages(callback) {
     if (this.isImagesRevised) {
-      callback();
+      if (callback) {
+        callback();
+      }
       return;
     }