RCS1139 Doesn't respect partial classes

I met with similar situation like #402.

1. `` on the main part of the class.
2. `` on any additional partials that require separate documentation.

RCS1139 displayed on the partial class file where only the `` was there.

Start by reviewing the RCS1139 implementation and comparing this report with issue #402. Reproduce the case with a summary on the main partial class and remarks on another partial, then verify that the diagnostic is not reported solely because the additional partial lacks a summary.

Written by the indexing model from the issue text.