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.
myisam/mi_packrec.c:
Fixed fill_buffer() to read byte by byte when the remaining
buffer size is less than word size.
mysql-test/r/myisampack.result:
Result file for BUG#41541
mysql-test/t/myisampack.test:
Testcase for BUG#41541
