While adjusting the coding style, three stupid mistakes happened.  The
quality is _not_ just 1, 2, 3, but really 1, 3, 2.  And the macros
ZYWRLE_PACK_COEFF() and ZYWRLE_UNPACK_COEFF() expand to more than one
statement, which means that we need curly brackets around them when they
are in an if clause.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>