The graph builder for Minimax M3 (build_minimaxm3.cpp) was not passing
model.layers[il].ffn_up_gate_exps to llm_build_std_moe_ffn, unlike
Minimax M2 and all other MoE model graph builders.
When -muge (merge_up_gate_experts) is enabled, the merge creates a single
ffn_up_gate_exps tensor with ffn_up_exps and ffn_gate_exps as views.
Only the parent merged tensor gets the split 'extra' pointer set.
Without passing it as up_gate_exps parameter, the function sees null
split pointers for up/gate (the views) while split_down_exps is valid,
causing the assertion at llama-build-context.cpp:1453 to fail.