Silence warning when initialising compress

Silence warning when initialising compress

The string literal initialalising compressed was too big for the
array as it has an unwanted NUL terminator.  This is allowed for
in C for historical reasons but produces a warning with some
compilers.  Adjust the declaration to include the NUL and adjust
the users to pass in an adjusted size which excludes the NUL rather
than sizeof(compressed).