Description:
------------
In pdo_firebird from CVS, calling PDOStatement->closeCursor on an executed statement that did *NOT* return any data kills the process.

Reproduce code:
---------------
<?php
	$pdo = new PDO( 'firebird:dbname=localhost:devel', 'devel', 'devel' );
	
	// VARIANT A: SECONDARY DATA
	$stmt = $pdo->prepare( 'UPDATE "a_data" SET "data"=200 RETURNING "a"' );
	$stmt->execute();
	
	// the following statement works fine
	$stmt->closeCursor();
	echo "I survived variant 'A'\n";
	
	// VARIANT B: REALLY NO DATA
	$stmt = $pdo->prepare( 'UPDATE "a_data" SET "data"=200' );
	$stmt->execute();
	
	// the following statement kills the process
	$stmt->closeCursor();
	echo "I don't survive upto here...\n";
?>

Expected result:
----------------
I survived variant 'A'
I don't survive upto here...

(Both statements executed an closeCursor called twice)

Actual result:
--------------
I survived variant 'A'

(Variant 'B' - the non-data statement - kills the process before echo.)