[ticket/13124] Also trim spaces in front of comments except for first line

PHPBB3-13124
[ticket/13124] Fix tests for event exporter

PHPBB3-13124
[ticket/13124] Add another test case as requested

PHPBB3-13124
Merge pull request #3024 from marc1706/ticket/13124

[ticket/13124] Also trim spaces in front of comments except for first line