the mpStr and mnLength arguments are always created from an OUString
and the OUString aRun(rArgs.mpStr); creates a duplicate of the original
string. Its way faster to pass the original OUString around instead.

Change-Id: I3de0cc31654eb215362548b6aee435f9c0c3c9db
Reviewed-on: https://gerrit.libreoffice.org/19221Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>