Ensure push token update job runs to completion

Promises must be retained.

// FREEBIE

Signal/src/Models/SyncPushTokensJob.swift

@@ -11,6 +11,8 @@ class SyncPushTokensJob : NSObject {
     let accountManager: AccountManager
     let preferences: PropertyListPreferences
     var uploadOnlyIfStale = true
+    // useful to ensure promise runs to completion
+    var retainCycle: SyncPushTokensJob?
 
     required init(pushManager: PushManager, accountManager: AccountManager, preferences: PropertyListPreferences) {
         self.pushManager = pushManager
@@ -29,29 +31,32 @@ class SyncPushTokensJob : NSObject {
 
     func run() -> Promise<Void> {
         Logger.debug("\(TAG) Starting.")
+        // Make sure we don't GC until completion.
+        self.retainCycle = self
 
         // Required to potentially prompt user for notifications settings
         // before `requestPushTokens` will return.
         self.pushManager.validateUserNotificationSettings()
 
         return self.requestPushTokens().then { (pushToken: String, voipToken: String) in
-
-            if self.preferences.getPushToken() == pushToken && self.preferences.getVoipToken() == voipToken {
-                Logger.debug("\(self.TAG) push tokens are already up to date.")
-                if (self.uploadOnlyIfStale) {
-                    return Promise { fulfill, reject in  fulfill(); }
-                } else {
-                    Logger.debug("\(self.TAG) proceeding with upload even though tokens aren't stale")
-                }
-            } else {
+            var shouldUploadTokens = !self.uploadOnlyIfStale
+            if self.preferences.getPushToken() != pushToken || self.preferences.getVoipToken() != voipToken {
                 Logger.debug("\(self.TAG) push tokens changed.")
+                shouldUploadTokens = true
+            }
+
+            guard shouldUploadTokens else {
+                Logger.info("\(self.TAG) skipping push token upload")
+                return Promise(value: ())
             }
 
-            Logger.debug("\(self.TAG) Sending new tokens to account servers.")
+            Logger.info("\(self.TAG) Sending new tokens to account servers.")
             return self.accountManager.updatePushTokens(pushToken:pushToken, voipToken:voipToken).then {
                 Logger.info("\(self.TAG) Recording tokens locally.")
-                return self.recordNewPushTokens(pushToken:pushToken, voipToken:voipToken);
+                return self.recordNewPushTokens(pushToken:pushToken, voipToken:voipToken)
             }
+        }.always {
+            self.retainCycle = nil
         }
     }