Do not fail backup creation when sticker files are missing.

app/src/main/java/org/thoughtcrime/securesms/backup/BackupFileIOError.java

@@ -58,9 +58,7 @@ public enum BackupFileIOError {
 
     if (error != null) {
       error.postNotification(context);
-    }
-
-    if (error == null) {
+    } else {
       UNKNOWN.postNotification(context);
     }
   }

app/src/main/java/org/thoughtcrime/securesms/backup/FullBackupExporter.java

@@ -54,6 +54,7 @@ import org.thoughtcrime.securesms.util.TextSecurePreferences;
 import org.thoughtcrime.securesms.util.Util;
 
 import java.io.File;
+import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
@@ -376,9 +377,11 @@ public class FullBackupExporter extends FullBackupBase {
     }
 
     if (!TextUtils.isEmpty(data) && size > 0) {
+      EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count, estimatedCount));
       try (InputStream inputStream = openAttachmentStream(attachmentSecret, random, data)) {
-        EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count, estimatedCount));
         outputStream.write(new AttachmentId(rowId, uniqueId), inputStream, size);
+      } catch (FileNotFoundException e) {
+        Log.w(TAG, "Missing attachment: " + e.getMessage());
       }
     }
 
@@ -402,6 +405,8 @@ public class FullBackupExporter extends FullBackupBase {
       EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count, estimatedCount));
       try (InputStream inputStream = ModernDecryptingPartInputStream.createFor(attachmentSecret, random, new File(data), 0)) {
         outputStream.writeSticker(rowId, inputStream, size);
+      } catch (FileNotFoundException e) {
+        Log.w(TAG, "Missing sticker: " + e.getMessage());
       }
     }