cli: fix empty block uploading in `util upload-bin` #1538

Job	Run time
Check internal dependencies	11s
Check code generated with 'go generate' is up-to-date	18s
CodeQL (go)	2m 32s
Coverage	7m 6s
Run tests (ubuntu-22.04, 1.22)	7m 31s
Run tests (windows-2022, 1.23)	23m 41s
Run tests (macos-12, 1.23)	12m 42s
Run tests (macos-14, 1.23)	15m 1s
Lint: interop / Lint	12s
Lint: NeoGo / Lint	37s
Lint: scripts / Lint	24s
Lint: examples (engine) / Lint	9s
Lint: examples (events) / Lint	12s
Lint: examples (iterator) / Lint	9s
Lint: examples (nft-d) / Lint	11s
Lint: examples (oracle) / Lint	10s
Lint: examples (nft-nd) / Lint	13s
Lint: examples (runtime) / Lint	11s
Lint: examples (nft-nd-nns) / Lint	23s
Lint: examples (storage) / Lint	10s
Lint: examples (token) / Lint	11s
Lint: examples (timer) / Lint	13s
Lint: examples (zkp/cubic_circuit) / Lint	15s
Lint: examples (zkp/xor_compat) / Lint	14s
	1h 12m 56s

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