fix the metadata parsing to be more robust so drracket does not crash when opening a corrupt htdp teaching language file closes PR 11332
fix the metadata parsing to be more robust so drracket does not crash when opening a corrupt htdp teaching language file
closes PR 11332

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