Fix #1211 PDOStatement::queryString not being set when using the regular PDOStatement

To explain this a hypothetical case is probably the best:
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Let's say you have a class "Custom_PDOStatement" which extends PDOStatement.
In this case you want the constructor to be called.
In PDOStatement you don't want the constructor to be called, because it would only throw an error,
that you shouldn't create a PDOStatement manually.

Current Problem
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The constructor is only being set when also the constructor is being called, 
which makes no sense, because you want queryString to be set in either case.