Prevent SQL Exception When Regenerating Session ID

RE: yiisoft/yii#2491
Added a value (empty string) for the `data` column when inserting a new row into the session table; the `data` column does not allow null values nor does it have a default value assigned so the CDbCommand::insert() method was throwing an exception when the SQL command failed.
Update Indentation Style

Update the indentation style from spaces to tabs, as per the Yii Framework guidelines.
Merge pull request #2493 from mynameiszanders/2491-sql-exception-regenerating-session-id

Prevent SQL Exception When Regenerating Session ID