Description:
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Pie chart images is not loaded. Only placeholder thumbs loaded. 

I checked the code and revised the lines and worked.

Reproduce code:
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I checked the code and revised the lines(Line~444) below;

    header("Content-type: image/png");
    imagepng($image);
    exit;

As:

        if(ob_get_length()>0) ob_clean();
	ob_start();
	header("Content-type: image/png");
	imagepng($image);
	ob_end_flush();