Enforce an higher "r_xassetnum" value

[TheFrenchGhosty]

Some mods use a ton of materials, this cause issue because when running some maps, the clients will crash.

Ideally the clients should have an higher r_xassetnum value.

This works on a server:

r_xassetnum "material=2560 xmodel=2048 xanim=3200 image=3000"

[IceNinjaman]

Can't raise material limit that easy, sorry.