BF: return NULL from failed Py3 module check
BF: return NULL from failed Py3 module check

Return NULL rather than bare return from Python 3 module check.

This causes clang to error during build of form:

  scipy/sparse/linalg/dsolve/_superlumodule.c:334:2: error: non-void
  function 'PyInit__superlu' should return a value [-Wreturn-type]

            return;

See:
https://s3.amazonaws.com/archive.travis-ci.org/jobs/205184825/log.txt

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