llama : fix empty batch causing llama_batch_allocr to crash (#9966)
* llama : fix empty batch cause llama_batch_allocr to crash
* move batch_allocr inside decode/encode_internal
* fix build
* add GGML_ASSERT
* Apply suggestions from code review
Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>