Handle JMP END case in MED synth

Lepeltheme from Sonic Solutions has a JMP END sequence in the synth
wave table without a valid parameter for JMP. Handle this in the same
way we handle END.

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

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