Problem with large file.

[truechernyshov]

Server is down with 503 error when loading big pdf(8Mb, 40 pages).
It's because you puting file in construct method Imagick.

$this->imagick = new Imagick($pdfFile);

But why whole file if i need only one page. In method getImageData there is instruction that page is need use for generate preview.

$this->imagick->readImage(sprintf('%s[%s]', $this->pdfFile, $this->page - 1));

If you need read all file don't indicate index of page. Like this:

$this->imagick->readImage($this->pdfFile);

After then i deleted file from constructor Imagick

$this->imagick = new Imagick();

And all works fine. If you want pick another page there is method setPage

[freekmurze]

I'd accept a test that fixes this. Alle current tests should pass.

[ArroWsGM]

@freekmurze, can you please review this PR #171