Fix recently introduced bug in selectevery
Fix recently introduced bug in selectevery

vapoursynth/vapoursynth,vapoursynth/vapoursynth,vapoursynth/vapoursynth,Kamekameha/vapoursynth,Kamekameha/vapoursynth,vapoursynth/vapoursynth,Kamekameha/vapoursynth,Kamekameha/vapoursynth