Do not fail backup when missing attachments.

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

@@ -376,8 +376,8 @@ public class FullBackupExporter extends FullBackupBase {
       }
     }
 
+    EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count, estimatedCount));
     if (!TextUtils.isEmpty(data) && size > 0) {
-      EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count, estimatedCount));
       try (InputStream inputStream = openAttachmentStream(attachmentSecret, random, data)) {
         outputStream.write(new AttachmentId(rowId, uniqueId), inputStream, size);
       } catch (FileNotFoundException e) {
@@ -423,6 +423,8 @@ public class FullBackupExporter extends FullBackupBase {
       while ((read = inputStream.read(buffer, 0, buffer.length)) != -1) {
         result += read;
       }
+    } catch (FileNotFoundException e) {
+      Log.w(TAG, "Missing attachment: " + e.getMessage());
     }
 
     return result;