Fix decals not appearing when a projectile with 0 size (blaster, crylink, hagar)...

Fix decals not appearing when a projectile with 0 size (blaster, crylink, hagar) hits a surface with a small angle. This fix also improves the previous fix for the same issue for hitscan weapons (1db2592)

Now the w_backoff factor is 2 for all weapons, except for the hook (-2) whose bomb explodes slightly below the floor