BUG: Fix _spectral_helper negative axis logic
BUG: Fix _spectral_helper negative axis logic

lhilt/scipy,mdhaber/scipy,aeklant/scipy,ilayn/scipy,pizzathief/scipy,lhilt/scipy,grlee77/scipy,Eric89GXL/scipy,scipy/scipy,endolith/scipy,perimosocordiae/scipy,grlee77/scipy,rgommers/scipy,mdhaber/scipy,scipy/scipy,aarchiba/scipy,WarrenWeckesser/scipy,jamestwebber/scipy,anntzer/scipy,matthew-brett/scipy,person142/scipy,ilayn/scipy,anntzer/scipy,gertingold/scipy,aeklant/scipy,scipy/scipy,anntzer/scipy,nmayorov/scipy,apbard/scipy,vigna/scipy,vigna/scipy,jor-/scipy,tylerjereddy/scipy,pizzathief/scipy,lhilt/scipy,mdhaber/scipy,Eric89GXL/scipy,jamestwebber/scipy,aeklant/scipy,jamestwebber/scipy,anntzer/scipy,apbard/scipy,apbard/scipy,scipy/scipy,mdhaber/scipy,endolith/scipy,rgommers/scipy,e-q/scipy,rgommers/scipy,gertingold/scipy,apbard/scipy,WarrenWeckesser/scipy,jamestwebber/scipy,perimosocordiae/scipy,scipy/scipy,pizzathief/scipy,WarrenWeckesser/scipy,andyfaff/scipy,rgommers/scipy,e-q/scipy,pizzathief/scipy,mdhaber/scipy,vigna/scipy,WarrenWeckesser/scipy,aeklant/scipy,anntzer/scipy,person142/scipy,tylerjereddy/scipy,arokem/scipy,apbard/scipy,nmayorov/scipy,lhilt/scipy,aarchiba/scipy,Stefan-Endres/scipy,lhilt/scipy,Eric89GXL/scipy,perimosocordiae/scipy,tylerjereddy/scipy,gfyoung/scipy,andyfaff/scipy,matthew-brett/scipy,matthew-brett/scipy,tylerjereddy/scipy,Eric89GXL/scipy,rgommers/scipy,gfyoung/scipy,Stefan-Endres/scipy,perimosocordiae/scipy,gertingold/scipy,aarchiba/scipy,grlee77/scipy,pizzathief/scipy,aeklant/scipy,endolith/scipy,e-q/scipy,e-q/scipy,gertingold/scipy,zerothi/scipy,zerothi/scipy,nmayorov/scipy,arokem/scipy,arokem/scipy,vigna/scipy,zerothi/scipy,jor-/scipy,zerothi/scipy,arokem/scipy,aarchiba/scipy,tylerjereddy/scipy,andyfaff/scipy,jor-/scipy,matthew-brett/scipy,ilayn/scipy,jor-/scipy,aarchiba/scipy,ilayn/scipy,vigna/scipy,ilayn/scipy,matthew-brett/scipy,nmayorov/scipy,nmayorov/scipy,e-q/scipy,endolith/scipy,andyfaff/scipy,WarrenWeckesser/scipy,endolith/scipy,gertingold/scipy,zerothi/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,zerothi/scipy,perimosocordiae/scipy,Stefan-Endres/scipy,arokem/scipy,endolith/scipy,person142/scipy,grlee77/scipy,jamestwebber/scipy,Eric89GXL/scipy,mdhaber/scipy,scipy/scipy,Eric89GXL/scipy,andyfaff/scipy,person142/scipy,gfyoung/scipy,andyfaff/scipy,ilayn/scipy,anntzer/scipy,grlee77/scipy,person142/scipy,gfyoung/scipy,jor-/scipy,Stefan-Endres/scipy,perimosocordiae/scipy,gfyoung/scipy