Fixed invalid variable

The details are as follows.
* https://github.com/processing/processing/pull/2318#issuecomment-42760306
* https://github.com/processing/processing/commit/a6dd50f1d1ad2044a7a71fb066b1f79eaf2c074b#diff-ef6cde1b12a1f443fa35d7b6c33b684eR774