Fix for divide by 0 exception when there is no interleave-moe-layer-step for llama4

[hongxiayang]

Fix the case where if interleave-moe-layer-step is 0, the code will throw div by 0 error.

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[houseroad]

Let's go with #17315?

[hongxiayang]

Let's go with #17315?

sure. seems these two PRS are exactly the same. haha.