The test started failing following the push for BUG#41541.
Some of the algorithms access bytes beyond the input data
and this can affect up to one byte less than "word size"
which is BITS_SAVED / 8.
Fixed by adding (BITS_SAVED / 8) -1 bytes to buffer size
(i.e. Memory Segment #2) to avoid accessing un-allocated data.
After the table is compressed by the myisampack utility,
opening the table by the server produces valgrind warnings.
This happens because when we try to read a record into the buffer
we alway assume that the remaining buffer to read is always equal
to word size(4 or 8 or 2 bytes) we read. Sometimes we have
remaining buffer size less than word size and trying to read the
entire word size will end up in valgrind errors.
Fixed by reading byte by byte when we detect the remaining buffer
size is less than the word size.
With certain data sets (when compressed record length gets bigger than
uncompressed) myisamchk --unpack may corrupt data file.
Fixed that record length was wrongly restored from compressed table.
