Theory: in previous versions, dither struct was static, which by definetion means its initiallized as all O's.  However, i removed static from the dither structbut then its not initialized.  Thus dithering started with some random stuff in the bit buckets.  Should be fixed now.

git-svn-id: https://svn.musicpd.org/mpd/trunk@1578 09075e82-0dd4-0310-85a5-a0d7c8717e4f