don't copy stylesheet's HelpID if this's a rename

This causes problems for renamed copies of std. styles, as they have
special handling in SdStyleSheet::SetHelpId, which would set the API
name to std. value too. That means that there would be two (or more)
stylesheets with the same API name. On export, only one of them would be
exported.

Change-Id: I19d243bd3f73995e8de2d251e3d8b7f93219c3a9
limit scope of variable

Change-Id: I74ccd6c8a3cfd45929973f21418458f3a83243af