Slightly adjust z-values calculated in the vertex shader so OGL does not clip the
final rendering of (at least) Sonic Unleashed.
This should be (nearly) invisible in Z16 depth copies and in games, but there is
some chance that it collides with other such border cases. There probably is some
room to decrease the adjustment but 9999999/10000000 is not enough. A static offset
may be an option, too. I don’t know if the game can/does set something like that.