[Kernel] Fix einsum operator for empty inputs #9677

Job	Run time
precheck	1m 55s
wasm_Debug / build-wasm	54m 22s
wasm_Release_static_library / build-wasm	7m 35s
wasm_Release / build-wasm	50m 37s
web_Release / build_onnxruntime_web	23m 17s
web_Debug / build_onnxruntime_web	18m 37s
	2h 36m 23s

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