Fix NPE in syncWithRemoteQueue when message is removed during sync (#485)

Add null check for localMessage after re-fetching from storage to guard
against a race condition where the message is removed between the
existence check and the retrieval.

Fixes #485

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sumchattering

iterableapi/src/main/java/com/iterable/iterableapi/IterableInAppManager.java

@@ -353,12 +353,14 @@ private void syncWithRemoteQueue(List<IterableInAppMessage> remoteQueue) {
             if (isInAppStored) {
                 IterableInAppMessage localMessage = storage.getMessage(message.getMessageId());
 
-                boolean shouldOverwriteInApp = !localMessage.isRead() && message.isRead();
+                if (localMessage != null) {
+                    boolean shouldOverwriteInApp = !localMessage.isRead() && message.isRead();
 
-                if (shouldOverwriteInApp) {
-                    localMessage.setRead(message.isRead());
+                    if (shouldOverwriteInApp) {
+                        localMessage.setRead(message.isRead());
 
-                    changed = true;
+                        changed = true;
+                    }
                 }
             }
         }