Safe showPendingMessage when there is no current activity

Author: Minishlink

android/src/main/java/tech/bam/RNBatchPush/RNBatchModule.java

@@ -157,9 +157,14 @@ public void push_getLastKnownPushToken(Promise promise) {
     // MESSAGING MODULE
 
     private void showPendingMessage() {
+        Activity activity = getCurrentActivity();
+        if (activity == null) {
+            return;
+        }
+
         BatchMessage message = Batch.Messaging.popPendingMessage();
         if (message != null) {
-            Batch.Messaging.show(getCurrentActivity(), message);
+            Batch.Messaging.show(activity, message);
         }
     }