android: fix crash in tile provider while closing the document

The problem was that for large documents if "back" was pressed quickly,
then we closed the document, but rendering thumbnails for the different
parts was still in progress.

Just make sure we don't crash when the underlying document is gone.

E/AndroidRuntime( 8902): java.lang.NullPointerException
E/AndroidRuntime( 8902):        at org.libreoffice.LOKitTileProvider.thumbnail(LOKitTileProvider.java:244)
E/AndroidRuntime( 8902):        at org.libreoffice.ThumbnailCreator$ThumbnailCreationTask.getThumbnail(ThumbnailCreator.java:78)
E/AndroidRuntime( 8902):        at org.libreoffice.LOKitThread.createThumbnail(LOKitThread.java:170)
E/AndroidRuntime( 8902):        at org.libreoffice.LOKitThread.processEvent(LOKitThread.java:148)
E/AndroidRuntime( 8902):        at org.libreoffice.LOKitThread.run(LOKitThread.java:120)

Change-Id: I93e8e1ea19545ca196ef6f59d19528bb42f3676d

1 files changed, 8 insertions, 1 deletions

diff --git a/android/experimental/LOAndroid3/src/java/org/libreoffice/LOKitTileProvider.java b/android/experimental/LOAndroid3/src/java/org/libreoffice/LOKitTileProvider.java
index 0970bbbc2a0c..78a592bce704 100644
--- a/android/experimental/LOAndroid3/src/java/org/libreoffice/LOKitTileProvider.java
+++ b/android/experimental/LOAndroid3/src/java/org/libreoffice/LOKitTileProvider.java
@@ -241,7 +241,8 @@ public class LOKitTileProvider implements TileProvider, Document.MessageCallback
         Log.w(LOGTAG, "Thumbnail size: " + getPageWidth() + " " + getPageHeight() + " " + widthPixel + " " + heightPixel);
 
         ByteBuffer buffer = ByteBuffer.allocateDirect(widthPixel * heightPixel * 4);
-        mDocument.paintTile(buffer, widthPixel, heightPixel, 0, 0, (int) mWidthTwip, (int) mHeightTwip);
+        if (mDocument != null)
+            mDocument.paintTile(buffer, widthPixel, heightPixel, 0, 0, (int) mWidthTwip, (int) mHeightTwip);
 
         Bitmap bitmap = Bitmap.createBitmap(widthPixel, heightPixel, Bitmap.Config.ARGB_8888);
         bitmap.copyPixelsFromBuffer(buffer);
@@ -287,12 +288,18 @@ public class LOKitTileProvider implements TileProvider, Document.MessageCallback
 
     @Override
     public void changePart(int partIndex) {
+        if (mDocument == null)
+            return;
+
         mDocument.setPart(partIndex);
         resetDocumentSize();
     }
 
     @Override
     public int getCurrentPartNumber() {
+        if (mDocument == null)
+            return 0;
+
         return mDocument.getPart();
     }