anv: incorrect task shader payload

Whenever the number of spawned mesh shaders triggers task redistribution threshold (currently 9), the redistributed mesh threads get uninitialized Task URB Entry. The only thing that works is disabling task distribution completely.

Reproducer in crucible@fa6e4adf.

Workaround in !16197 (merged).

Windows driver doesn't hit this.

(Opened on request by @cmarcelo)