Fix for optional tag sets vanishing on edit

Fix for issue 2729 https://code.google.com/p/otwarchive/issues/detail?id=2729 : optional tag sets vanished on edit.

Signed-off-by: shalott <shalott@gmail.com>
Merge pull request #1321 from shalott/issue_2729_save_opt_tags

Fix for optional tag sets vanishing on edit