Don't touch empty wallpaper sentinel every backup.

Even when the diffing algorithm is good (which it may not always be),
it isn't free to apply the diff server side.

Test: manual
Change-Id: I01859a57b0a0a974b541ce03f7c35a2977df7f7c

1 files changed, 4 insertions, 2 deletions

diff --git a/packages/WallpaperBackup/src/com/android/wallpaperbackup/WallpaperBackupAgent.java b/packages/WallpaperBackup/src/com/android/wallpaperbackup/WallpaperBackupAgent.java
index 4254a0ba200a..2e40c1acfa2c 100644
--- a/packages/WallpaperBackup/src/com/android/wallpaperbackup/WallpaperBackupAgent.java
+++ b/packages/WallpaperBackup/src/com/android/wallpaperbackup/WallpaperBackupAgent.java
@@ -115,8 +115,10 @@ public class WallpaperBackupAgent extends BackupAgent {
             // We always back up this 'empty' file to ensure that the absence of
             // storable wallpaper imagery still produces a non-empty backup data
             // stream, otherwise it'd simply be ignored in preflight.
-            FileOutputStream touch = new FileOutputStream(empty);
-            touch.close();
+            if (!empty.exists()) {
+                FileOutputStream touch = new FileOutputStream(empty);
+                touch.close();
+            }
             fullBackupFile(empty, data);
 
             SharedPreferences prefs = getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);