Handle null DownloadManager

If the DownloadManager has been disabled by the user via Settings for
instance, DownloadManager can be null, so MediaProvider should handle
it gracefully

Test: Manual
Bug: 178679250
Merged-In: If7b94298f281a31ffb6b4f829161c5f5dc44317d
Change-Id: I313f1239d1551cdbff6a58e35769d3495eb043da
diff --git a/src/com/android/providers/media/MediaProvider.java b/src/com/android/providers/media/MediaProvider.java
index 6b485e3..9e1efa5 100644
--- a/src/com/android/providers/media/MediaProvider.java
+++ b/src/com/android/providers/media/MediaProvider.java
@@ -4772,8 +4772,10 @@
                 // Do this on a background thread, since we don't want to make binder
                 // calls as part of a FUSE call.
                 helper.postBackground(() -> {
-                    getContext().getSystemService(DownloadManager.class)
-                            .onMediaStoreDownloadsDeleted(deletedDownloadIds);
+                    DownloadManager dm = getContext().getSystemService(DownloadManager.class);
+                    if (dm != null) {
+                        dm.onMediaStoreDownloadsDeleted(deletedDownloadIds);
+                    }
                 });
             }