Merge pull request #5088 from ethereum-optimism/sc/fd-correct-length

fix(fd): use correct fn for getTotalElements

.changeset/three-apes-study.md

+---
+'@eth-optimism/fault-detector': patch
+---
+
+Fixes a bug that would cause the fault detector to error out if no outputs had been proposed yet.

packages/fault-detector/src/service.ts

@@ -124,7 +124,7 @@ export class FaultDetector extends BaseServiceV2<Options, Metrics, State> {
       this.state.oo = {
         contract: oo,
         filter: oo.filters.OutputProposed(),
-        getTotalElements: async () => oo.latestOutputIndex(),
+        getTotalElements: async () => oo.nextOutputIndex(),
         getEventIndex: (args) => args.l2OutputIndex,
       }
     } else {