fix(loadtest): Do not initiate transactions with 0 amount (#1847)

## What ❔

Makes sure that any transaction has amount of 1 wei at least.

## Why ❔

- It is no longer possible to withdraw 0 wei, so the test became flaky.
- Testing edge cases is not a point for loadtest, we have integration
tests for that.

## Checklist

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- [ ] Tests for the changes have been added / updated.
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core/tests/loadnext/src/command/tx_command.rs

@@ -189,6 +189,6 @@ impl TxCommand {
     }
 
     fn random_amount(rng: &mut LoadtestRng) -> U256 {
-        rng.gen_range(0u64..2u64.pow(18)).into()
+        rng.gen_range(1u64..2u64.pow(18)).into()
     }
 }