Fix resume called on app start (#526)

Author: nzagorchev

LeanplumSDK/LeanplumSDK/Classes/Internal/Leanplum.m

@@ -1103,7 +1103,9 @@ + (void)addUIApplicationObservers
                     //if they are changed the new valeus will be updated to server as well
                     [[Leanplum notificationsManager] updateNotificationSettings];
 
-                    [Leanplum resume];
+                    if ([Leanplum hasStarted]) {
+                        [Leanplum resume];
+                    }
 
                     // Used for push notifications iOS 9
                     [Leanplum notificationsManager].proxy.resumedTimeInterval = [[NSDate date] timeIntervalSince1970];