[Android] Fix NPE in setSmallIcon when iconResourceId is null

[mtallenca]

Description

Fixes a NullPointerException that crashes the app when a scheduled notification is delivered on Android.

setSmallIcon falls into its legacy backwards-compat branch when the notification has no icon and no persisted default icon in shared preferences. That branch then calls:

builder.setSmallIcon(notificationDetails.iconResourceId);

iconResourceId is a boxed Integer, so passing it to setSmallIcon(int) auto-unboxes it. When it is null, this throws:

Fatal Exception: java.lang.RuntimeException: Unable to start receiver
  com.dexterous.flutterlocalnotifications.ScheduledNotificationReceiver:
  java.lang.NullPointerException: Attempt to invoke virtual method
  'int java.lang.Integer.intValue()' on a null object reference
    at ...FlutterLocalNotificationsPlugin.setSmallIcon(FlutterLocalNotificationsPlugin.java:490)
    at ...FlutterLocalNotificationsPlugin.createNotification(FlutterLocalNotificationsPlugin.java:391)
    at ...FlutterLocalNotificationsPlugin.showNotification(FlutterLocalNotificationsPlugin.java:1297)
    at ...ScheduledNotificationReceiver.onReceive(ScheduledNotificationReceiver.java:61)

How a notification reaches this state

ScheduledNotificationReceiver.onReceive deserializes the NotificationDetails payload that was persisted at schedule time. A notification serialized by an older version of the plugin (before the notification carried an icon string) deserializes with both icon == null and iconResourceId == null. If that alarm fires after the app has been updated — but before the app has run initialize() again to persist a default icon — all three fall-throughs are hit and the receiver crashes on delivery. This is especially common on devices that auto-update apps in the background without ever being launched.

Fix

Guard the null iconResourceId in the legacy branch and fall back to the application's own icon (context.getApplicationInfo().icon), which is always a valid resource for an installed app, so notification delivery never crashes.

Fixes #298
Fixes #2049

Type of Change

• 🐛 Bug Fix (non-breaking change which fixes an issue)