Correct output format of iron
Correct output format of iron

If nnz of input matrices is zero, the output of iron defaulted to the format "coo" even if explicitly given otherwise (see issue #13099)
e-q/scipy,Eric89GXL/scipy,scipy/scipy,Stefan-Endres/scipy,vigna/scipy,endolith/scipy,andyfaff/scipy,zerothi/scipy,grlee77/scipy,Eric89GXL/scipy,endolith/scipy,mdhaber/scipy,WarrenWeckesser/scipy,Stefan-Endres/scipy,zerothi/scipy,matthew-brett/scipy,mdhaber/scipy,anntzer/scipy,rgommers/scipy,rgommers/scipy,ilayn/scipy,rgommers/scipy,perimosocordiae/scipy,anntzer/scipy,WarrenWeckesser/scipy,matthew-brett/scipy,Stefan-Endres/scipy,rgommers/scipy,matthew-brett/scipy,vigna/scipy,WarrenWeckesser/scipy,andyfaff/scipy,ilayn/scipy,perimosocordiae/scipy,andyfaff/scipy,andyfaff/scipy,Stefan-Endres/scipy,endolith/scipy,zerothi/scipy,anntzer/scipy,Stefan-Endres/scipy,endolith/scipy,grlee77/scipy,zerothi/scipy,vigna/scipy,WarrenWeckesser/scipy,zerothi/scipy,WarrenWeckesser/scipy,anntzer/scipy,mdhaber/scipy,andyfaff/scipy,tylerjereddy/scipy,scipy/scipy,perimosocordiae/scipy,andyfaff/scipy,ilayn/scipy,tylerjereddy/scipy,Eric89GXL/scipy,zerothi/scipy,endolith/scipy,mdhaber/scipy,mdhaber/scipy,vigna/scipy,ilayn/scipy,e-q/scipy,vigna/scipy,Eric89GXL/scipy,e-q/scipy,grlee77/scipy,scipy/scipy,tylerjereddy/scipy,Stefan-Endres/scipy,scipy/scipy,ilayn/scipy,Eric89GXL/scipy,grlee77/scipy,tylerjereddy/scipy,e-q/scipy,grlee77/scipy,WarrenWeckesser/scipy,scipy/scipy,mdhaber/scipy,Eric89GXL/scipy,anntzer/scipy,rgommers/scipy,tylerjereddy/scipy,matthew-brett/scipy,ilayn/scipy,perimosocordiae/scipy,endolith/scipy,perimosocordiae/scipy,matthew-brett/scipy,anntzer/scipy,scipy/scipy,perimosocordiae/scipy,e-q/scipy