FIX division by zero

[mwehr]

Hi,

This fixes division by zero in case a new thumbnail needs to be generated.

kind regards,
Mario

[aolley]

This will reduce performance when viewing galleries as it always loads the image metadata.

It'd be preferable to simply load this data when its actually needed to generate a new thumbnail as opposed to always.

[mwehr]

We have the problem that in case if a new thumbnail is needed, and "Show extended image info" is "No" the width and height are 0.
So the division in the get_image_resized() #320 throws a division by zero.

Another option would be to leave the "if" clause and additionally check for an empty "thumbnail"

if (is_null($thumbnail) ||  $loadextrainfo) {
    $imageinfo = $this->storedfile->get_imageinfo();
    $this->height = $imageinfo['height'];
    $this->width = $imageinfo['width'];
}

What do you think ?