Remove end of note flag on new note

When computing a new note in FT2, ST3 or MOD modes, reset the end of
note flag.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Update envelope reset test data

Update data to reflect fixes in portamento envelope reset.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix note end after fadeout finishes

Don't reset the virtual channel when fadeout ends, the data may be
used by a new event with portamento effect.

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