Hello vtpup
It would be quite a simple case of installing a .pet of this little library which is an extra loader for gdk-pixbuf. Viewnior uses gdk-pixbuf to display the images so it is not a case of patching viewnior.
Thanks to norgo for confirming that it works.
The developer does seem to be tinkering around with it over the last few days with versions 0.1.x and 0.2.0 which looks like a bit of a fundamental rewrite/rethink, so it might be worth hanging on a bit and keeping an eye to see if he does more updates.
I tried it in my Stretch Pup and 0.2.0 did give an error in compiling.
As Burunduk reported, version 0.0.7 compiles and works OK though.