Exclude images from lightbox in "Photo Swipe Masonry"

i am using the "Photo Swipe Masonry" plugin (version 1.0.6) on wordpress 4.3.1. It works perfect so far.

But, i have some images which have a custom link to an external url(instead of the stadard to the image). If i click one of these images, it opens the url in a new window. That works like expected. Now, when i click on an standard image(no external url), the lightbox opens and the image is displayed like expected.

But now, when i use the prev/next buttons to navigate through the images and i reach an image with a custom link, i got the errormessage:

"The image could not be loaded" (in the lightbox).

So, my question is, how to exclude images from being added to the lightbox? Maybe by a unique class ?

Any help is highly appreciated.

Many thanks in advance to all of you for your time.

Regards, Joe

via Chebli Mohamed