Actually fail when an error occurs in parseFormat

[antlarr]

When there's an unsupported number of bits per sample or an invalid number of samples per block, don't only print an error message using the error handler, but actually stop parsing the file.

This fixes #35 (also reported at https://bugzilla.opensuse.org/show_bug.cgi?id=1026983 and https://blogs.gentoo.org/ago/2017/02/20/audiofile-heap-based-buffer-overflow-in-imadecodeblockwave-ima-cpp/ )