Fix validator's activity api handler.

beacon_chain/validator_client/api.nim

@@ -1937,7 +1937,12 @@ proc getValidatorsActivity*(
   let resp = vc.onceToAll(RestPlainResponse, SlotDuration,
                           {BeaconNodeRole.Duties},
                           getValidatorsActivity(it, epoch, validators))
+  if len(resp.data) == 0:
     case resp.status
+    of ApiOperation.Success:
+      # This should not be happened, there should be present at least one
+      # successfull response.
+      return GetValidatorsActivityResponse()
     of ApiOperation.Timeout:
       debug "Unable to perform validator's activity request in time",
             timeout = SlotDuration
@@ -1948,7 +1953,7 @@ proc getValidatorsActivity*(
     of ApiOperation.Failure:
       debug "Unexpected error happened while receiving validator's activity"
       return GetValidatorsActivityResponse()
-  of ApiOperation.Success:
+  else:
     var activities: seq[RestActivityItem]
     for apiResponse in resp.data:
       if apiResponse.data.isErr():