rpcclient: always provide `start` parameter for `findstorage` RPC #151

Job	Run time
Coverage	9m 47s
CodeQL (go)	6m 23s
Check internal dependencies	6s
Lint	55s
Run tests (ubuntu-20.04, 1.19)	10m 28s
Run tests (ubuntu-20.04, 1.20)	11m 30s
Run tests (windows-2022, 1.21)	25m 44s
Run tests (macos-12, 1.21)	10m 24s
	1h 15m 17s

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