move eob_reached logic into ff_lzw_decode_tail() which simplifies the code, avoids some checks in the innermost loop and also gets rid of the controversal break while hopefully retaining the last byte in a valid bytestream, invalid bytestreams still can have very significant overread


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@8517 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b