fix: don't panic on empty sync assignments

Author: LuccaBitfly

backend/pkg/api/services/service_slot_viz.go

@@ -228,6 +228,9 @@ func (s *Services) updateSlotVizData() error {
 				dutiesInfo.SlotSyncParticipated[duty.Slot] = make(map[constypes.ValidatorIndex]bool, 0)
 
 				partValidators := utils.GetParticipatingSyncCommitteeValidators(duty.SyncAggregateBits, dutiesInfo.TotalSyncAssignmentsForEpoch[utils.EpochOfSlot(duty.Slot)])
+				if len(partValidators) == 0 {
+					log.Error(nil, "no participating sync validators found", 0, map[string]interface{}{"slot": duty.Slot})
+				}
 				for _, validator := range partValidators {
 					dutiesInfo.SlotSyncParticipated[duty.Slot][validator] = true
 				}

backend/pkg/commons/utils/utils.go

@@ -221,6 +221,9 @@ func SortedUniqueUint64(arr []uint64) []uint64 {
 }
 
 func GetParticipatingSyncCommitteeValidators(syncAggregateBits []byte, validators []uint64) []uint64 {
+	if len(validators) != len(syncAggregateBits)*8 {
+		return nil
+	}
 	participatingValidators := []uint64{}
 	for i := 0; i < len(syncAggregateBits)*8; i++ {
 		val := validators[i]