DDMsgReader: Bug fix for deleting multiple selected messages

Eric Oulashinrequested to merge
dd_msg_reader_multiple_msg_delete_hdr_fix into master

DDMsgReader: Bug fix for deleting multiple selected messages: When updating message headers in the cached arrays, don't try to save them back to the database, because that was already done (this avoids a 'header has expanded fields' error).

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