Photoswipe loading pictures twice when opened via picture link

[DanielMuller]

Reported by @laklare in #22. Created new issue for easier tracking.

This is minor, but the number of total photos that Photoswipe reports always seems to be double when the URL links directly to a photo (contains a pid and gid). For instance, if I copy the URL for the first image in an album containing 30 photos (1/30), the Photoswipe lightbox will says 1/60. At least in Pillar-based themes.