asn1: Avoid calling malloc with 0 argument
asn1: Avoid calling malloc with 0 argument

Caused problems reported by oss-fuzz

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=18758

fabled/OpenSC,rickyepoderi/OpenSC,CardContact/OpenSC,mouse07410/OpenSC,OpenSC/OpenSC,mouse07410/OpenSC,metsma/OpenSC,Jakuje/OpenSC,LudovicRousseau/OpenSC,dengert/OpenSC,metsma/OpenSC,Jakuje/OpenSC,philipWendland/OpenSC,OpenSC/OpenSC,CardContact/OpenSC,dengert/OpenSC,hongquan/OpenSC-main,hongquan/OpenSC-main,philipWendland/OpenSC,hongquan/OpenSC-main,LudovicRousseau/OpenSC,AktivCo/OpenSC,LudovicRousseau/OpenSC,frankmorgner/OpenSC,fabled/OpenSC,CardContact/OpenSC,frankmorgner/OpenSC,Jakuje/OpenSC,fabled/OpenSC,frankmorgner/OpenSC,fabled/OpenSC,OpenSC/OpenSC,Jakuje/OpenSC,rickyepoderi/OpenSC,metsma/OpenSC,frankmorgner/OpenSC,dengert/OpenSC,rickyepoderi/OpenSC,mouse07410/OpenSC,philipWendland/OpenSC,AktivCo/OpenSC,AktivCo/OpenSC