fix: Don't overwrite existing folders (#284)

Don't overwrite existing folders

Author: felixrieseberg

lib/filesystem.js

@@ -51,7 +51,7 @@ class Filesystem {
     if (shouldUnpack) {
       node.unpacked = shouldUnpack
     }
-    node.files = {}
+    node.files = node.files || {}
     return node.files
   }