vm: fix MODPOW operation #1579

Job	Run time
Check internal dependencies	11s
Check code generated with 'go generate' is up-to-date	14s
CodeQL (go)	2m 54s
Run tests (ubuntu-22.04, 1.22)	7m 18s
Coverage	7m 18s
Run tests (windows-2022, 1.23)	21m 47s
Run tests (macos-12, 1.23)	14m 44s
Run tests (macos-14, 1.23)	17m 2s
Lint: NeoGo / Lint	52s
Lint: interop / Lint	14s
Lint: scripts / Lint	16s
Lint: examples (engine) / Lint	7s
Lint: examples (events) / Lint	7s
Lint: examples (iterator) / Lint	8s
Lint: examples (nft-d) / Lint	7s
Lint: examples (nft-nd) / Lint	7s
Lint: examples (nft-nd-nns) / Lint	13s
Lint: examples (oracle) / Lint	13s
Lint: examples (runtime) / Lint	13s
Lint: examples (storage) / Lint	14s
Lint: examples (timer) / Lint	7s
Lint: examples (token) / Lint	13s
Lint: examples (zkp/cubic_circuit) / Lint	10s
Lint: examples (zkp/xor_compat) / Lint	13s
	1h 15m 2s

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