Description:
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imagegd2 does not produce valid gd2 image if used under output control

Reproduce code:
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$strBinary = file_get_contents('test.jpg');
$resHandle = imagecreatefromstring($strBinary);
ob_start();
imagegd2($resHandle);
$strBinary2 = ob_get_clean();
imagecreatefromstring($strBinary2);

>>>imagecreatefromstring($strBinary2) issues warning but following works fine:

$strBinary = file_get_contents('test.jpg');
$resHandle = imagecreatefromstring($strBinary);
imagegd2($resHandle, 'test.gd2');
$strBinary2 = file_get_contents('test.gd2');
imagecreatefromstring($strBinary2); 

Expected result:
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nothing

Actual result:
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second call to imagecreatefromstring issues
function.imagecreatefromstring: Passed data is not in 'GD2' format