fix androidx lifecycle causes analytics init in background crash (#824)

* fix androidx lifecycle causes analytics init in background crash

* fix typo

analytics/src/main/java/com/segment/analytics/Analytics.java

@@ -352,7 +352,12 @@ public void run() {
 
         application.registerActivityLifecycleCallbacks(activityLifecycleCallback);
         if (useNewLifecycleMethods) {
-            lifecycle.addObserver(activityLifecycleCallback);
+            // NOTE: addObserver is required to run on UI thread,
+            // though we made it compatible to run from background thread,
+            // there is a chance that lifecycle events get lost if init
+            // analytics from background (i.e. analytics is init, but
+            // lifecycle hook is yet to be registered.
+            run(() -> lifecycle.addObserver(activityLifecycleCallback));
         }
     }
 
@@ -799,6 +804,15 @@ public void run() {
                 });
     }
 
+    private void run(Runnable runnable) {
+        if (Looper.myLooper() == Looper.getMainLooper()) {
+            runnable.run();
+        }
+        else {
+            HANDLER.post(runnable);
+        }
+    }
+
     /**
      * Asynchronously flushes all messages in the queue to the server, and tells bundled
      * integrations to do the same.
@@ -1000,7 +1014,7 @@ public void shutdown() {
         application.unregisterActivityLifecycleCallbacks(activityLifecycleCallback);
         if (useNewLifecycleMethods) {
             // only unregister if feature is enabled
-            lifecycle.removeObserver(activityLifecycleCallback);
+            run(() ->lifecycle.removeObserver(activityLifecycleCallback));
         }
         // Only supplied by us for testing, so it's ok to shut it down. If we were to make this
         // public,