Fix build

SignalServiceKit/src/Loki/Protocol/Multi Device/MultiDeviceProtocol.swift

@@ -64,7 +64,6 @@ public final class MultiDeviceProtocol : NSObject {
             }
         }
         return threadPromise.then2 { thread -> Promise<Void> in
-        return threadPromise.then(on: OWSDispatch.sendingQueue()) { thread -> Promise<Void> in
             let message = messageSend.message
             let messageSender = SSKEnvironment.shared.messageSender
             let (promise, seal) = Promise<Void>.pending()
@@ -73,7 +72,9 @@ public final class MultiDeviceProtocol : NSObject {
                 && message.shouldBeSaved() // shouldBeSaved indicates it isn't a transient message
             if !shouldSendAutoGeneratedFR {
                 let messageSendCopy = copy(messageSend, for: destination, with: seal)
-                messageSender.sendMessage(messageSendCopy)
+                OWSDispatch.sendingQueue().async {
+                    messageSender.sendMessage(messageSendCopy)
+                }
             } else {
                 Storage.write { transaction in
                     getAutoGeneratedMultiDeviceFRMessageSend(for: destination.hexEncodedPublicKey, in: transaction, seal: seal)
@@ -131,7 +132,9 @@ public final class MultiDeviceProtocol : NSObject {
         }.catch2 { error in
             // Proceed even if updating the recipient's device links failed, so that message sending
             // is independent of whether the file server is online
-            messageSender.sendMessage(messageSend)
+            OWSDispatch.sendingQueue().async {
+                messageSender.sendMessage(messageSend)
+            }
         }
     }