am a3d1e94e: Merge "Fix bug where constructing message attachment uri with null/empty partId will remove the trailing backslash, causing the uri to not match the expected pattern." into jb-ub-mail-ur9

* commit 'a3d1e94ebc4d5a1bab1d9f6ac7de962f8eeebd1b':
  Fix bug where constructing message attachment uri with null/empty partId will remove the trailing backslash, causing the uri to not match the expected pattern.