Fix crashing in LokiApi.

SignalServiceKit/src/Loki/LokiAPI.swift

@@ -1,5 +1,19 @@
 import PromiseKit
 
+// Helper function for objc apis
+private extension Promise where T == Any {
+    func recoverNetworkError(on queue: DispatchQueue) -> Promise<T> {
+        return self.recover(on: queue) { error -> Promise<T> in
+            switch error {
+            case NetworkManagerError.taskError(_, let underlyingError):
+                throw underlyingError
+            default:
+                throw error
+            }
+        }
+    }
+}
+
 @objc public final class LokiAPI : NSObject {
     
     private static let version = "v1"
@@ -68,13 +82,16 @@ import PromiseKit
     // MARK: Obj-C API
     @objc public static func objc_getMessages() -> AnyPromise {
         let promise = getMessages()
+            .recoverNetworkError(on: DispatchQueue.global())
         let anyPromise = AnyPromise(promise)
         anyPromise.retainUntilComplete()
         return anyPromise
     }
     
     @objc public static func objc_sendSignalMessage(_ signalMessage: SignalMessage, to destination: String, requiringPoW isPoWRequired: Bool) -> AnyPromise {
-        let promise = LokiMessage.fromSignalMessage(signalMessage, requiringPoW: isPoWRequired).then(sendMessage)
+        let promise = LokiMessage.fromSignalMessage(signalMessage, requiringPoW: isPoWRequired)
+            .then(sendMessage)
+            .recoverNetworkError(on: DispatchQueue.global())
         let anyPromise = AnyPromise(promise)
         anyPromise.retainUntilComplete()
         return anyPromise