[ticket/12079] Add default value to $multibyte in request.untrimmed_variable().

PHPBB3-12079
Merge pull request #1940 from prototech/ticket/12079

[ticket/12079] Add default value to $multibyte in request.untrimmed_varible().

* prototech/ticket/12079:
  [ticket/12079] Add default value to $multibyte in request.untrimmed_variable().