Read 32-bit MED4 sample length

MED4 supports samples larger than 64 KB. Read the sample length as a
32 bit value (fixes jackatta.med from ftp.modland.com)

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update changelog

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>