possible need for note-off and note-on prioritizing

[atsushieno]

When I was authoring some phrase like this:

1   @30 o4 V110 v100 l8 RSD20 DSD40
    Kc+Kf+
    [ fg(50g)50g^2.b4a4f4 : fg(50g)50g^1. ]2  fg(50g)50g^1f2  [r-1]8
    [ de(50e)50e^2.g4f4d4 : de(50e)50e^1. ]2  de(50e)50e^1d2  [r-1]8
    < [ ab(50b)50b^2.>e4d4<a4 : ab(50b)50b^1. ]2  ab(50b)50b^1a2

It is like, I wanted to enter each note on the tritone (possibly quadtone, after this) chords respectively and entered MML like this, making use of [r-1] to roll back. However at the end of the fourth bar (at b4a4f4 bar), only a4 is noted on.

It is because the other chord notes emit note-offs, resulting that the first note-on events (e.g. b4a4f4) are suppressed by the following note-offs of the chord note sequence (e.g. g4f4d4, note that f4 is connected).

It can be easily workarounded if the song gives q operation e.g. q1 but that's not ideal.

[atsushieno]

Solution:

• (1) detect and warn about zero-length note operations. It has points because this kind of problems may happen in other use cases, but does not resolve the present issue.
• (2) detect zero-length note operations and alter note-on/off operations by prioritizing them, if applicable. It should exactly resolve the problem, but complicates the MML processing rules.