Detect RIFF files with invalid chunk sizes

The bug report has a WAVE file with zero-sized 'data' chunk, which causes
TagLib to iterate over the file, 8 bytes in each iteration. The new code
adds a check for the chunk name, which forces it to mark the file as
invalid if the chunk name doesn't contain ASCII characters.

https://bugs.kde.org/show_bug.cgi?id=283412