base64: Improve error handling
base64: Improve error handling

tempbottle/coreutils,Shir0kamii/coreutils,dennis/coreutils,jbcrail/coreutils,bundai223/coreutils,hexsel/coreutils,Gianbaoluo/coreutils,bundai223/coreutils,keunwoo/coreutils,silvio/rust-coreutils,wimh/coreutils,dbrgn/coreutils,dokaptur/coreutils,kball/coreutils,polapl/coreutils,samfoo/coreutils,efuquen/coreutils,tempbottle/coreutils,efuquen/coreutils,retep998/coreutils,steveklabnik/coreutils,Arcterus/coreutils,Shir0kamii/coreutils,kevgeniy/coreutils,hexsel/coreutils,silvio/rust-coreutils,kevgeniy/coreutils,mauricio/coreutils,jbcrail/coreutils,uutils/coreutils,beni55/coreutils,Shtong/coreutils,wimh/coreutils,kwantam/coreutils,filmor/coreutils,beni55/coreutils,Heather/coreutils,sshling/coreutils,kball/coreutils,sshling/coreutils,samfoo/coreutils,filmor/coreutils,dbrgn/coreutils,Shtong/coreutils,dbrgn/coreutils,keunwoo/coreutils,mauricio/coreutils,ebfe/coreutils,uutils/coreutils,Arcterus/coreutils,polapl/coreutils,kwantam/coreutils,dennis/coreutils,steveklabnik/coreutils,ebfe/coreutils,uutils/coreutils,retep998/coreutils,Gianbaoluo/coreutils,Heather/coreutils