[MP] Rend2: Update to ioquake/ioq3@375f6247d4faf4a2a4d14885213d1cf7516b453d , ioquake/ioq3@b099255748edaec547242e7f165c4016a8bad69b

Also fixes bug where leftover `len` variable was being set still for no reason in R_LoadVisibility.