Draw ALL of the particles, not just 2/3 of them.

Using quads requires 4 elements, but triangles require 6. I'd gotten the
element array setup right, but I'd forgotten to tweak vacount when drawing
the particles.

libs/video/renderer/glsl/glsl_particles.c

@@ -1616,7 +1616,7 @@ draw_qf_particles (void)
 			VectorAdd (part->org, up_right_scale, VA[3].vertex);
 
 			VA += 4;
-			vacount += 4;
+			vacount += 6;
 		}
 
 		part->phys (part);