Fix off-by-one in LZW decoding

See
http://lists.openmicroscopy.org.uk/pipermail/ome-users/2014-July/004566.html
One more indexing fix for LZW
Merge pull request #1224 from melissalinkert/rebased/dev_5_0/lzw-fix

Fix off-by-one in LZW decoding (rebased onto dev_5_0)