Don't retry proof of work calculation

SignalServiceKit/src/Loki/API/LokiAPI.swift

@@ -73,11 +73,10 @@ public final class LokiAPI : NSObject {
             return invoke(.sendMessage, on: target, associatedWith: destination, parameters: parameters)
         }
         func sendLokiMessageUsingSwarmAPI() -> Promise<Set<RawResponsePromise>> {
-            let powPromise = lokiMessage.calculatePoW()
-            let swarmPromise = getTargetSnodes(for: destination)
-            return when(fulfilled: powPromise, swarmPromise).map { lokiMessageWithPoW, swarm in
-                return Set(swarm.map {
-                    sendLokiMessage(lokiMessageWithPoW, to: $0).map { rawResponse in
+            return lokiMessage.calculatePoW().then { lokiMessageWithPoW in
+                return getTargetSnodes(for: destination).map { swarm in
+                    return Set(swarm.map { target in
+                        sendLokiMessage(lokiMessageWithPoW, to: target).map { rawResponse in
                             if let json = rawResponse as? JSON, let powDifficulty = json["difficulty"] as? Int {
                                 guard powDifficulty != LokiAPI.powDifficulty else { return rawResponse }
                                 print("[Loki] Setting proof of work difficulty to \(powDifficulty).")
@@ -90,6 +89,7 @@ public final class LokiAPI : NSObject {
                     })
                 }.retryingIfNeeded(maxRetryCount: maxRetryCount)
             }
+        }
         if let peer = LokiP2PAPI.getInfo(for: destination), (lokiMessage.isPing || peer.isOnline) {
             let target = LokiAPITarget(address: peer.address, port: peer.port)
             return Promise.value([ target ]).mapValues { sendLokiMessage(lokiMessage, to: $0) }.map { Set($0) }.retryingIfNeeded(maxRetryCount: maxRetryCount).get { _ in