Description:
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when I try to use ImagickDraw to draw a filled arc, using the 
same color for fill as for stroke on a new image with opaque 
black background, it resets image background to transparent

Reproduce code:
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<?php

$image = new \Imagick();
$image->newImage(400, 300, '#000000');

$pixel = new \ImagickPixel('#ffffff');
$pixel->setColorValue(\Imagick::COLOR_OPACITY, 0.0);

$arc = new \ImagickDraw();

$arc->setStrokeColor($pixel);
$arc->setStrokeWidth(1);
$arc->setFillColor($pixel);
$arc->arc(50, 50, 350, 250, 45, 135);

$image->drawImage($arc);
$image->flattenImages()->writeImage('/path/to/arc.png');

$pixel->clear();
$pixel->destroy();

$arc->clear();
$arc->destroy();


Expected result:
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Should draw a white chord on a black background

Actual result:
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Draws a white chord on a transparent background