.it global sample volume is broken

[AliceLR]

This .it file contains two copies of the same sample with different global sample volumes that are played at different pitches. When played in Impulse Tracker, one low sample can be heard clearly; when it's played with xmp, both samples can be heard equally loud. libxmp seems to treat the global sample volume as maximum.

global_sample_volume.it.zip

[AliceLR]

Fixing this seems to be a matter of

1. Enabling QUIRK_INSVOL in sample mode (it_load.c, line 1120)

	if (sample_mode || ifh.cmwt >= 0x200) {
		m->quirk |= QUIRK_INSVOL;
	}

2. Setting the volume of the fake instruments that get generated in sample mode (it_load.c, line 783)

	if (sample_mode) {
		/* Create an instrument for each sample */
		mod->xxi[i].vol = 64;

I don't know how this would affect old format .its though.

[AliceLR]

It looks like load_it_sample assigns the subinstrument global volume to the sample global volume regardless of the IT format version. QUIRK_INSVOL must be enabled to apply subinstrument global volume (https://github.com/libxmp/libxmp/blob/master/src/player.c#L736) so as far as I can tell QUIRK_INSVOL should be applied unconditionally to IT modules.

This should still be verified with an old format IT module.

[AliceLR]

Here's an IT 1.x module with instrument mode enabled that very obviously relies on sample global volume (in one of the drums, but much more noticeably with the vocal samples). IT 1.06, IT 2.14, and OpenMPT all play these samples at a lower volume than xmp. When I change this patch to unconditionally enable QUIRK_INSVOL xmp also plays it correctly.

https://modland.com/pub/modules/Impulsetracker/Ranger%20Rick/witness.it

Current patch here: master...AliceLR:fix-it-sample-volume-vibrato. The vibrato part of this patch (#103) still needs to be verified.