After some researching, I can confirm the reason of the black particle problem is glitched modulate shader on some graphic driver, with the "$mod2x 1" config. So, I choose a new fixing method: make the corresponding vmt not rendering. It's more effective than previous method (modifying particle system file). Maybe it can eliminate more glitched particle in game.

Fix broken gas station fire after explosion in No Mercy because of the original add-on's file.

Rework on the L4D2 particle system file instead of orginal add-on's L4D1 file to avoid bad efffect onburning zombie.