Increase minigun low-ammo click sound threshold

[anf3is]

• From default 6 to 8 (12 to 16) - increase by 33%. 25% would be better, but we work with int.
• Close Low ammo sound treshholds too low for some weapons? #278

[WhenTanksFly]

I've just re-checked the issue at hand, turns out I was wrong, please see the updated issue discussion thread.