Fix crash when uploading file

src/apps.js

@@ -2000,7 +2000,8 @@ function uploadFile(appId, sourceFilePath, destFilePath, callback) {
 
     const done = once(function (error) {
         safe.fs.unlinkSync(sourceFilePath); // remove file in /tmp
-        callback(new BoxError(BoxError.FS_ERROR, error.message)); // blame it on filesystem for now
+        if (error) return callback(new BoxError(BoxError.FS_ERROR, error.message)); // blame it on filesystem for now
+        callback(null);
     });
 
     // the built-in bash printf understands "%q" but not /usr/bin/printf.