avoid getting stuck on non-UTF-8 symbol encodings in bytecode
avoid getting stuck on non-UTF-8 symbol encodings in bytecode

Found by fuzz tester, and this bug seems to be a common reason for
the fuzz test to time out.

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