[benchmarks] Guard empty metrics on verifier runs.

[ysiraichi]

This PR fixes result_analyzer.py by guarding its metric processing function call get_calculated_metrics, checking whether it's empty or not.

Empty metrics was allowed on results.jsonl starting on #7777, where verifier-only runs were enabled.

cc @miladm @zpcore

[zpcore]

LGTM!

[zpcore]

We can add the python result_analyzer.py ... in the test:

xla/test/benchmarks/run_torchbench_tests.sh

Lines 74 to 96 in b4335f8

	function run_tests {
	local overall_status=0
	local pjrt_device="CPU"
	# TODO(piz): Uncomment the following if we decide to run on GPU.
	# if [ -x "$(command -v nvidia-smi)" ]; then
	# num_devices=$(nvidia-smi --list-gpus | wc -l)
	# echo "Found $num_devices GPU devices..."
	# export GPU_NUM_DEVICES=$num_devices
	# pjrt_device="CUDA"
	# fi
	for model in "${TORCHBENCH_MODELS[@]}"; do
	echo "testing model: $model"
	PJRT_DEVICE=$pjrt_device python -u benchmarks/experiment_runner.py \
	--suite-name=torchbench \
	--experiment-config='{"accelerator":"'"$pjrt_device"'","xla":"PJRT","dynamo":"openxla","test":"eval","torch_xla2":null,"xla_flags":null,"keep_model_data_on_cuda":false}' \
	--model-config='{"model_name":"'"$model"'"}'
	if [ $? -ne 0 ]; then
	echo "ERROR: Failed to test $model. Exiting with failure." >&2
	overall_status=1
	else
	success_count=$((success_count + 1))
	fi
	done

just to be safe.

[ysiraichi]

I will leave that to a follow-up PR.