in .vgm export, panning values are inverted for OKI MSM6258

[damifortune]

it functions correctly in the tracker (v0.6.7), but when exported to .vgm, if you have used a panning macro or an effect command to control the panning of the OKI MSM6258 sampler channel, the panning values are the opposite of what they should be.

for example, if you have panned it to the left, it will be panned right in the .vgm, and vice versa. crucially, if you have turned both channels back on, it becomes muted. 08FF mutes both the left and right stereo, panning macro value '3' (which should be both on) also mutes both the left and right stereo.

the behavior is slightly different for 0800 effect, which never turns both channels back on, versus setting a panning macro of '0' for an instrument which does restore both the left and right stereo to playback.

so aside from that 0800 quirk, they seem to just be inverted in the .vgm export - 3 should be 0, 2 should be 1, 1 should be 2, and 0 should be 3. attached a simple example with both .fur and exported .vgm.

msm6258_pan_test.zip