Added the CDbCommand::throwExceptionIfSqlQueryTextExists() method

[JustMisha]

This method is called by the methods that populate the $_query array to prevent hard to debug errors.

If __construct() or setText sets $_text there is no point in using the methods like select(), from(), etc after that because the sql query text already exists and the buildQuery() method will never be called.

[marcovtwout]

Thanks for your PR, but Yii 1 is only accepting compatibility and security fixes as it is in maintainance mode. Also I understand why you would want the framework to prevent this kind of misusage of the query builder, but this is not something we can change easily and keep backward compatible.