[ticket/11106] Undefined index EDITED_TIME_TOTAL notice.

When viewing a private message, when message edit count is 1
Undefined index EDITED_TIME_TOTAL php notice appears. Changed
the message formatting method to what is used in viewtopic.php.

PHPBB3-11106
[ticket/11106] Added missing line breaks.

Added two missing line breaks into 'edited by' message.

PHPBB3-11106
Merge pull request #1287 from erangamapa/ticket/11106

[ticket/11106] Undefined index EDITED_TIME_TOTAL notice.