fix: Use a null prototype object for this.files

This approach is taken to prevent overriding object methods that would
exist on a normal object Object.create({})

Author: MichaelAquilina

lib/index.js

@@ -19,7 +19,10 @@ function JSZip() {
     //   "folder/" : {...},
     //   "folder/data.txt" : {...}
     // }
-    this.files = {};
+    // NOTE: we use a null prototype because we do not
+    // want filenames like "toString" coming from a zip file
+    // to overwrite methods and attributes in a normal Object.
+    this.files = Object.create(null);
 
     this.comment = null;
 

lib/object.js

@@ -179,16 +179,16 @@ var out = {
      */
     forEach: function(cb) {
         var filename, relativePath, file;
+        /* jshint ignore:start */
+        // ignore warning about unwanted properties because this.files is a null prototype object
         for (filename in this.files) {
-            if (!this.files.hasOwnProperty(filename)) {
-                continue;
-            }
             file = this.files[filename];
             relativePath = filename.slice(this.root.length, filename.length);
             if (relativePath && filename.slice(0, this.root.length) === this.root) { // the file is in the current root
                 cb(relativePath, file); // TODO reverse the parameters ? need to be clean AND consistent with the filter search fn...
             }
         }
+        /* jshint ignore:end */
     },
 
     /**