added -existing- to error message to help programmers understand that they must specify the name of an existing file
added -existing- to error message to help programmers understand that they must specify the name of an existing file

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket